The Potential for Treatment Shortening With Higher Rifampicin Doses: Relating Drug Exposure to Treatment Response in Patients With Pulmonary Tuberculosis

High-Dose Rifampicin for 3 Months after Culture Conversion for Drug-Susceptible Pulmonary Tuberculosis

BACKGROUND

This study aimed to determine whether a shorter high-dose rifampicin regimen is non-inferior to the standard 6-month tuberculosis regimen.

METHODS

This multicenter, randomized, open-label, non-inferiority trial enrolled participants with respiratory specimen positivity by Xpert MTB/RIF assay or Mycobacterium tuberculosis culture without rifampicin-resistance. Participants were randomized at 1:1 to the investigational or control group. The investigational group received high-dose rifampicin (30 mg/kg/day), isoniazid, and pyrazinamide until culture conversion, followed by high-dose rifampicin and isoniazid for 12 weeks. The control group received the standard 6-month regimen. The primary outcome was the rate of unfavorable outcomes at 18 months post-randomization. The non-inferiority margin was set at <6% difference in unfavorable outcomes rates. The study is registered with ClinicalTrials.gov (NCT04485156).

RESULTS

Between 4 November 2020 and 3 January 2022, 76 participants were enrolled. Of these, 58 were included in the modified intention-to-treat analysis. Unfavorable outcomes occurred in 10 (31.3%) of 32 in the control group and 10 (38.5%) of 26 in the investigational group. The difference was 7.2% (95% confidence interval, ∞ to 31.9%), failing to prove non-inferiority. Serious adverse events and grade 3 or higher adverse events did not differ between the groups.

CONCLUSION

The shorter high-dose rifampicin regimen failed to demonstrate non-inferiority but had an acceptable safety profile.

A pharmacometric multistate model for predicting long-term treatment outcomes of patients with pulmonary TB

BACKGROUND

Studying long-term treatment outcomes of TB is time-consuming and impractical. Early and reliable biomarkers reflecting treatment response and capable of predicting long-term outcomes are urgently needed.

OBJECTIVES

To develop a pharmacometric multistate model to evaluate the link between potential predictors and long-term outcomes.

METHODS

Data were obtained from two Phase II clinical trials (TMC207-C208 and TMC207-C209) with bedaquiline on top of a multidrug background regimen. Patients were typically followed throughout a 24 week investigational treatment period plus a 96 week follow-up period. A five-state multistate model (active TB, converted, recurrent TB, dropout, and death) was developed to describe observed transitions. Evaluated predictors included patient characteristics, baseline TB disease severity and on-treatment biomarkers.

RESULTS

A fast bacterial clearance in the first 2 weeks and low TB bacterial burden at baseline increased probability to achieve conversion, whereas patients with XDR-TB were less likely to reach conversion. Higher estimated mycobacterial load at the end of 24 week treatment increased the probability of recurrence. At 120 weeks, the model predicted 55% (95% prediction interval, 50%-60%), 6.5% (4.2%-9.0%) and 7.5% (5.2%-10%) of patients in converted, recurrent TB and death states, respectively. Simulations predicted a substantial increase of recurrence after 24 weeks in patients with slow bacterial clearance regardless of baseline bacterial burden.

CONCLUSIONS

The developed multistate model successfully described TB treatment outcomes. The multistate modelling framework enables prediction of several outcomes simultaneously, and allows mechanistically sound investigation of novel promising predictors. This may help support future biomarker evaluation, clinical trial design and analysis.

Shortened Treatment Regimens for Drug Sensitive TB

Tuberculosis (TB) has remained a global health challenge despite the availability of effective anti-tubercular drugs and various treatment strategies. Apart from the complications related to TB disease per se, adverse effects of antitubercular therapy (ATT) also contribute to morbidity. In addition to the adverse effects, the long duration of the treatment regimen also reduces the patient's acceptability of ATT. The available "short-course treatment regimens" are still relatively long, thereby adversely affecting treatment compliance. There is a need for effective, safe, short and intensive regimens for TB which can reduce the treatment cost and adverse effects, thereby improving its acceptance. With the emergence of new evidence, the World Health Organization (WHO) has recently endorsed 4 mo short duration ATT regimen for non-severe, drug-sensitive cases of tuberculosis. Even in severe forms of disease like tubercular meningitis (TBM), trials are underway evaluating efficacy and safety of shorter regimens. Inclusion of fluroquinolones and rifapentine help shorten the regimens. These shortened regimens, however, need more close monitoring for adverse effects and may need to be converted to longer course if there is inadequate clinical response. Thus, shorter regimens for pediatric TB are likely to not only decrease the burden on patients and healthcare but also improve compliance and lower the side effects of the drugs due to prolonged exposure. This article reviews the current evidence and the guidelines pertaining to the shortened, intensive regimens for drug-sensitive tuberculosis.

Pharmacokinetic-Pharmacodynamic Evidence From a Phase 3 Trial to Support Flat-Dosing of Rifampicin for Tuberculosis

BACKGROUND

The optimal dosing strategy for rifampicin in treating drug-susceptible tuberculosis (TB) is still highly debated. In the phase 3 clinical trial Study 31/ACTG 5349 (NCT02410772), all participants in the control regimen arm received 600 mg rifampicin daily as a flat dose. Here, we evaluated relationships between rifampicin exposure and efficacy and safety outcomes.

METHODS

We analyzed rifampicin concentration time profiles using population nonlinear mixed-effects models. We compared simulated rifampicin exposure from flat- and weight-banded dosing. We evaluated the effect of rifampicin exposure on stable culture conversion at 6 months; TB-related unfavorable outcomes at 9, 12, and 18 months using Cox proportional hazard models; and all trial-defined safety outcomes using logistic regression.

RESULTS

Our model-derived rifampicin exposure ranged from 4.57 mg · h/L to 140.0 mg · h/L with a median of 41.8 mg · h/L. Pharmacokinetic simulations demonstrated that flat-dosed rifampicin provided exposure coverage similar to the weight-banded dose. Exposure-efficacy analysis (n = 680) showed that participants with rifampicin exposure below the median experienced similar hazards of stable culture conversion and TB-related unfavorable outcomes compared with those with exposure above the median. Exposure-safety analysis (n = 722) showed that increased rifampicin exposure was not associated with increased grade 3 or higher adverse events or serious adverse events.

CONCLUSIONS

Flat-dosing of rifampicin at 600 mg daily may be a reasonable alternative to the incumbent weight-banded dosing strategy for the standard-of-care 6-month regimen. Future research should assess the optimal dosing strategy for rifampicin, at doses higher than the current recommendation.

Safety and Efficacy of 25 mg/kg and 35 mg/kg vs 10 mg/kg Rifampicin in Pulmonary TB: A Phase IIb Randomized Controlled Trial

Background

Globally, no trial data are available on head-to-head comparison between 10 mg/kg and 25/35 mg/kg rifampicin in treating pulmonary tuberculosis during study initiation.

Methods

A multicentric, phase IIb randomized trial recruited 333 new culture-positive, drug-sensitive adult patients with pulmonary tuberculosis to compare safety and efficacy of high-dose rifampicin (R25/R35), against conventional dose (R10) given daily for 8 weeks followed by standard doses for 16 weeks. Main outcomes were treatment-emergent grade 3/4 adverse events (AEs) and time-to-culture conversion in liquid media, assessed by division of AIDS system for grading the severity of adverse events division of AIDS criteria and Kaplan-Meier methods.

Results

In a modified intention-to-treat population of 323 patients (R10: 105/R25: 112/R35: 106), grade 3/4 AEs were reported in 34 patients (R10: 9.5% [10/105], R25: 9.8% [11/112], R35: 12.3% [13/106]) during the intensive phase. Among 23 patients (R10: 3.8% [4/105], R25: 6.3% [7/112], R35: 11.3% [12/106]) with grade 3/4 hepatotoxicity, 15 (R10: 1.9% [2/105], R25: 3.6% [4/112], R35: 8.5% [9/106]) had grade 3/4 hyperbilirubinemia and 9 patients (R10: 1.0% [1/105], R25: 0.9% [1/112], R35: 6.6% [7/106]) developed clinical jaundice. Significant differences observed only between R10 and R35 with hepatotoxicity (P = .039), hyperbilirubinemia (P = .031), clinical jaundice (P = .032), and treatment interruption (P = .039). Eighteen serious AEs and 6 deaths (R10: 3/R25: 1/R35: 2) occurred during study period. Time to stable culture conversion in liquid media was faster in R25 (adjusted hazard ratio, 1.71; 95% confidence interval [CI], 1.26-2.31 [solid: 1.97; 95% CI, 1.46-2.67]) and R35 (1.81; 95% CI, 1.33-2.48 [solid: 2.24; 95% CI, 1.64-3.06]), than R10 (34 vs 44 days). R25 had no failure/relapse.

Conclusions

Hepatotoxicity, clinical jaundice, and treatment interruptions occurred significantly higher with R35 than R10. Because R25 was comparably safe as R10 and also highly efficacious than R10, it may be considered for implementation. Clinical Trials Registration. CTRI/2017/12/010951.

Standards for clinical trials for treating TB

BACKGROUND: The value, speed of completion and robustness of the evidence generated by TB treatment trials could be improved by implementing standards for best practice.METHODS: A global panel of experts participated in a Delphi process, using a 7-point Likert scale to score and revise draft standards until consensus was reached.RESULTS: Eleven standards were defined: Standard 1, high quality data on TB regimens are essential to inform clinical and programmatic management; Standard 2, the research questions addressed by TB trials should be relevant to affected communities, who should be included in all trial stages; Standard 3, trials should make every effort to be as inclusive as possible; Standard 4, the most efficient trial designs should be considered to improve the evidence base as quickly and cost effectively as possible, without compromising quality; Standard 5, trial governance should be in line with accepted good clinical practice; Standard 6, trials should investigate and report strategies that promote optimal engagement in care; Standard 7, where possible, TB trials should include pharmacokinetic and pharmacodynamic components; Standard 8, outcomes should include frequency of disease recurrence and post-treatment sequelae; Standard 9, TB trials should aim to harmonise key outcomes and data structures across studies; Standard 10, TB trials should include biobanking; Standard 11, treatment trials should invest in capacity strengthening of local trial and TB programme staff.CONCLUSION: These standards should improve the efficiency and effectiveness of evidence generation, as well as the translation of research into policy and practice.

A prognostic baseline blood biomarker and tumor growth kinetics integrated model in paclitaxel/platinum treated advanced non-small cell lung cancer patients

Paclitaxel/platinum chemotherapy, the backbone of standard first-line treatment of advanced non-small cell lung cancer (NSCLC), exhibits high interpatient variability in treatment response and high toxicity burden. Baseline blood biomarker concentrations and tumor size (sum of diameters) at week 8 relative to baseline (RS8) are widely investigated prognostic factors. However, joint analysis of data on demographic/clinical characteristics, blood biomarker levels, and chemotherapy exposure-driven early tumor response for improved prediction of overall survival (OS) is clinically not established. We developed a Weibull time-to-event model to predict OS, leveraging data from 365 patients receiving paclitaxel/platinum combination chemotherapy once every three weeks for ≤six cycles. A developed tumor growth inhibition model, combining linear tumor growth and first-order paclitaxel area under the concentration-time curve-induced tumor decay, was used to derive individual RS8. The median model-derived RS8 in all patients was a 20.0% tumor size reduction (range from -78% to +15%). Whereas baseline carcinoembryonic antigen, cytokeratin fragments, and thyroid stimulating hormone levels were not significantly associated with OS in a subset of 221 patients, and lactate dehydrogenase, interleukin-6 and neutrophil-to-lymphocyte ratio levels were significant only in univariate analyses (p value < 0.05); C-reactive protein (CRP) in combination with RS8 most significantly affected OS (p value < 0.01). Compared to the median population OS of 11.3 months, OS was 128% longer at the 5th percentile levels of both covariates and 60% shorter at their 95th percentiles levels. The combined paclitaxel exposure-driven RS8 and baseline blood CRP concentrations enables early individual prognostic predictions for different paclitaxel dosing regimens, forming the basis for treatment decision and optimizing paclitaxel/platinum-based advanced NSCLC chemotherapy.

Drug interaction potential of high-dose rifampicin in patients with pulmonary tuberculosis

Accumulating evidence supports the use of higher doses of rifampicin for tuberculosis (TB) treatment. Rifampicin is a potent inducer of metabolic enzymes and drug transporters, resulting in clinically relevant drug interactions. To assess the drug interaction potential of higher doses of rifampicin, we compared the effect of high-dose rifampicin (40 mg/kg daily, RIF40) and standard-dose rifampicin (10 mg/kg daily, RIF10) on the activities of major cytochrome P450 (CYP) enzymes and P-glycoprotein (P-gp). In this open-label, single-arm, two-period, fixed-order phenotyping cocktail study, adult participants with pulmonary TB received RIF10 (days 1-15), followed by RIF40 (days 16-30). A single dose of selective substrates (probe drugs) was administered orally on days 15 and 30: caffeine (CYP1A2), tolbutamide (CYP2C9), omeprazole (CYP2C19), dextromethorphan (CYP2D6), midazolam (CYP3A), and digoxin (P-gp). Intensive pharmacokinetic blood sampling was performed over 24 hours after probe drug intake. In all, 25 participants completed the study. Geometric mean ratios (90% confidence interval) of the total exposure (area under the concentration versus time curve, RIF40 versus RIF10) for each of the probe drugs were as follows: caffeine, 105% (96%-115%); tolbutamide, 80% (74%-86%); omeprazole, 55% (47%-65%); dextromethorphan, 77% (68%-86%); midazolam, 62% (49%-78%), and 117% (105%-130%) for digoxin. In summary, high-dose rifampicin resulted in no additional effect on CYP1A2, mild additional induction of CYP2C9, CYP2C19, CYP2D6, and CYP3A, and marginal inhibition of P-gp. Existing recommendations on managing drug interactions with rifampicin can remain unchanged for the majority of co-administered drugs when using high-dose rifampicin. Clinical Trials registration number NCT04525235.

Isoniazid and rifampicin exposure during treatment in drug-susceptible TB

BACKGROUND: Observational real-world studies on therapeutic drug monitoring (TDM) in relation to pharmacokinetic (PK) target values are lacking. This study aims to describe the PK of rifampicin (RIF) and isoniazid (INH) in a real-world setting of patients with drug-susceptible TB in relation to frequently used threshold values.METHODS: A total of 116 patients with TB using standard doses of RIF and INH and who had TDM as part of clinical care were included. Maximum plasma concentration (Cmax) and 24 h area under the concentration time curve (AUC24) at standard and revised doses were described in relation to the threshold values (Cmax ≥8 mg/L for RIF and ≥3 mg/L for INH).RESULTS: For RIF (100 patients), median Cmax and median AUC24 were respectively 7.9 mg/L (IQR 6.0-11.0) and 35.8 mg*h/L (IQR 27.4-57.3) at the first TDM measurement after a standard dose of 600 mg. For INH (90 patients), median Cmax and median AUC24 were respectively 2.9 mg/L (IQR 1.3-2.5) and 12.5 mg*h/L (IQR 8.7-18.9) at the first TDM after a standard dose 300 mg. Overall, more than 50% of study participants had drug exposure below threshold values at the first TDM.CONCLUSION: Our study shows that the measured Cmax values for both RIF and INH were frequently below the pre-specified targets, emphasising the need for better justification of drug exposure targets. These TDM results highlight the need for validating PK targets of anti-TB drugs associated with clinically relevant outcomes.

Four-Month High-Dose Rifampicin Regimens for Pulmonary Tuberculosis

BACKGROUND: Shorter but effective tuberculosis treatment regimens would be of value to the tuberculosis treatment community. High-dose rifampicin has been associated with more rapid and secure lung sterilization and may enable shorter tuberculosis treatment regimens. METHODS: We randomly assigned adults who were given a diagnosis of rifampicin-susceptible pulmonary tuberculosis to a 6-month control regimen, a similar 4-month regimen of rifampicin at 1200 mg/d (study regimen 1 [SR1]), or a 4-month regimen of rifampicin at 1800 mg/d (study regimen 2 [SR2]). Sputum specimens were collected at regular intervals. The primary end point was a composite of treatment failure and relapse in participants who were sputum smear positive at baseline. The noninferiority margin was 8 percentage points. Using a sequence of ordered hypotheses, noninferiority of SR2 was tested first. RESULTS: Between January 2017 and December 2020, 672 patients were enrolled in six countries, including 191 in the control group, 192 in the SR1 group, and 195 in the SR2 group. Noninferiority was not shown. Favorable responses rates were 93, 90, and 87% in the control, SR1, and SR2 groups, respectively, for a country-adjusted absolute risk difference of 6.3 percentage points (90% confidence interval, 1.1 to 11.5) comparing SR2 with the control group. The proportions of participants experiencing a grade 3 or 4 adverse event were 4.0, 4.5, and 4.4% in the control, SR1, and SR2 groups, respectively. CONCLUSIONS: Four-month high-dose rifampicin regimens did not have dose-limiting toxicities or side effects but failed to meet noninferiority criteria compared with the standard 6-month control regimen for treatment of pulmonary tuberculosis. (Funded by the MRC/Wellcome Trust/DFID Joint Global Health Trials Scheme; ClinicalTrials.gov number, NCT02581527.)

Pharmacokinetics of Efavirenz 600mg in Combination with Rifampicin in Chinese HIV/TB Co-Infection Patients

Background

Rifampicin is a known inducer of the cytochrome P450 (CYP2B6) enzyme, which can lead to a decrease in the concentration of efavirenz. Therefore, we conducted a study to evaluate the effect of daily rifampicin intake on efavirenz 600mg pharmacokinetics and HIV-1 virological suppression.

Methods

Patients receiving antiretroviral therapy containing efavirenz (600mg daily), and we collected efavirenz concentration at four visit points: ART day 14 (PK1), ART day 42 (PK2), ART day 140 (PK3), and ART day 336 (PK4), and performed pharmacokinetics analysis.

Results

From February 2017 to November 2020, 29 HIV/TB co-infection patients were included. Ninety percent of patients had a concentration of ≥1000ng/mL of efavirenz during the study. All patients had efavirenz C_max ≥1000ng/mL, 86% patients showed good virology response.

Conclusion

Our study shows that the use of rifampicin in HIV/TB co-infection patients does not affect efavirenz drug concentrations, that virological suppression is good and that no efavirenz dose adjustment is required.

Optimizing (O) rifapentine-based (RI) regimen and shortening (EN) the treatment of drug-susceptible tuberculosis (T) (ORIENT) using an adaptive seamless design: study protocol of a multicenter randomized controlled trial

BACKGROUND

Standard treatment for drug-susceptible tuberculosis (DS-TB) includes a multidrug regimen requiring at least 6 months of treatment, and this lengthy treatment easily leads to poor adherence. There is an urgent need to simplify and shorten treatment regimens to reduce interruption and adverse event rates, improve compliance, and reduce costs.

METHODS

ORIENT is a multicenter, randomized controlled, open-label, phase II/III, non-inferiority trial involving DS-TB patients to evaluate the safety and efficacy of short-term regimens compared with the standardized six-month treatment regimen. In stage 1, corresponding to a phase II trial, a total of 400 patients are randomly divided into four arms, stratified by site and the presence of lung cavitation. Investigational arms include 3 short-term regimens with rifapentine 10 mg/kg, 15 mg/kg, and 20 mg/kg, while the control arm uses the standardized six-month treatment regimen. A combination of rifapentine, isoniazid, pyrazinamide, and moxifloxacin is administered for 17 or 26 weeks in rifapentine arms, while a 26-week regimen containing rifampicin, isoniazid, pyrazinamide, and ethambutol is applied in the control arm. After the safety and preliminary effectiveness analysis of patients in stage 1, the control arm and the investigational arm meeting the conditions will enter into stage 2, which is equivalent to a phase III trial and will be expanded to recruit DS-TB patients. If all investigational arms do not meet the safety conditions, stage 2 will be canceled. In stage 1, the primary safety endpoint is permanent regimen discontinuation at 8 weeks after the first dose. The primary efficacy endpoint is the proportion of favorable outcomes at 78 weeks after the first dose for both two stages.

DISCUSSION

This trial will contribute to the optimal dose of rifapentine in the Chinese population and suggest the feasibility of the short-course treatment regimen containing high-dose rifapentine and moxifloxacin for DS-TB.

TRIAL REGISTRATION

The trial has been registered on ClinicalTrials.gov on 28 May 2022 with the identifier NCT05401071.

High rifampicin peak plasma concentrations accelerate the slow phase of bacterial decline in tuberculosis patients: Evidence for heteroresistance

BACKGROUND

Antibiotic treatments are often associated with a late slowdown in bacterial killing. This separates the killing of bacteria into at least two distinct phases: a quick phase followed by a slower phase, the latter of which is linked to treatment success. Current mechanistic explanations for the in vitro slowdown are either antibiotic persistence or heteroresistance. Persistence is defined as the switching back and forth between susceptible and non-susceptible states, while heteroresistance is defined as the coexistence of bacteria with heterogeneous susceptibilities. Both are also thought to cause a slowdown in the decline of bacterial populations in patients and therefore complicate and prolong antibiotic treatments. Reduced bacterial death rates over time are also observed within tuberculosis patients, yet the mechanistic reasons for this are unknown and therefore the strategies to mitigate them are also unknown.

METHODS AND FINDINGS

We analyse a dose ranging trial for rifampicin in tuberculosis patients and show that there is a slowdown in the decline of bacteria. We show that the late phase of bacterial killing depends more on the peak drug concentrations than the total drug exposure. We compare these to pharmacokinetic-pharmacodynamic models of rifampicin heteroresistance and persistence. We find that the observation on the slow phase's dependence on pharmacokinetic measures, specifically peak concentrations are only compatible with models of heteroresistance and incompatible with models of persistence. The quantitative agreement between heteroresistance models and observations is very good ([Formula: see text]). To corroborate the importance of the slowdown, we validate our results by estimating the time to sputum culture conversion and compare the results to a different dose ranging trial.

CONCLUSIONS

Our findings indicate that higher doses, specifically higher peak concentrations may be used to optimize rifampicin treatments by accelerating bacterial killing in the slow phase. It adds to the growing body of literature supporting higher rifampicin doses for shortening tuberculosis treatments.

Decreased Dolutegravir and Efavirenz Concentrations With Preserved Virological Suppression in Patients With Tuberculosis and Human Immunodeficiency Virus Receiving High-Dose Rifampicin

BACKGROUND

Higher doses of rifampicin may improve treatment outcomes and reduce the duration of tuberculosis (TB) therapy. However, drug-drug interactions with antiretroviral therapy (ART) and safety in people with human immunodeficiency virus (HIV) have not been evaluated.

METHODS

This was a randomized, open-label trial where newly diagnosed TB patients were randomized to higher (35 mg/kg) or standard (10 mg/kg) daily-dose rifampicin. ART treatment-naive patients were randomized to dolutegravir- or efavirenz-based ART. At week 6, trough dolutegravir or mid-dose efavirenz plasma concentrations were assayed. HIV viral load was measured at week 24.

RESULTS

Among 128 patients randomized, the median CD4 count was 191 cells/mm3. The geometric mean ratio (GMR) for trough dolutegravir concentrations on higher- vs standard-dose rifampicin was 0.57 (95% confidence interval [CI], .34-.97; P = .039) and the GMR for mid-dose efavirenz was 0.63 (95% CI, .38-1.07; P = .083). There was no significant difference in attainment of targets for dolutegravir trough or efavirenz mid-dose concentrations between rifampicin doses. The incidence of HIV treatment failure at week 24 was similar between rifampicin doses (14.9% vs 14.0%, P = .901), as was the incidence of drug-related grade 3-4 adverse events (9.8% vs 6%). At week 8, fewer patients remained sputum culture positive on higher-dose rifampicin (18.6% vs 37.0%, P = .063).

CONCLUSIONS

Compared with standard-dose rifampicin, high-dose rifampicin reduced dolutegravir and efavirenz exposures, but HIV suppression was similar across treatment arms. Higher-dose rifampicin was well tolerated among people with HIV and associated with a trend toward faster sputum culture conversion.

CLINICAL TRIALS REGISTRATION

NCT03982277.

Treatment shortening of drug-sensitive pulmonary tuberculosis using high-dose rifampicin for 3 months after culture conversion (Hi-DoRi-3): a study protocol for an open-label randomized clinical trial

BACKGROUND

The standard treatment regimen for drug-sensitive tuberculosis (TB), comprising four companion drugs, requires a minimum duration of 6 months, and this lengthy treatment leads to poor adherence and increased toxicity. To improve rates of adherence, reduce adverse events, and lower costs, a simplified and shortened treatment regimen is warranted.

METHODS

This study is a multicenter, open-label randomized clinical trial of non-inferiority design that compares a new regimen with the conventional regimen for drug-sensitive pulmonary TB. The investigational group will use a regimen of high-dose rifampicin (30 mg/kg/day) with isoniazid and pyrazinamide, and the treatment will be maintained for 12 weeks after the achievement of negative conversion of sputum culture. The control group will be treated for 6 months with a World Health Organization-endorsed regimen consisting of isoniazid, rifampicin (10 mg/kg/day), ethambutol, and pyrazinamide. The primary endpoint is the proportion of unfavorable outcomes at 18 months after randomization. Secondary outcomes include time to unfavorable treatment outcome, time to culture conversion on liquid medium, treatment success rate at the end of treatment, proportion of recurrence at 18 months after randomization, time to recurrence after treatment completion, and adverse events of grade 3 or higher during the treatment. We predict a 10% unfavorable outcome for the control group, and 0% difference from the investigational group. Based on 80% verification power and a 2.5% one-sided significance level for a non-inferiority margin of 6%, 393 participants per group are required. Considering the 15% dropout rate, a total of 926 participants (463 in each group) will be recruited.

DISCUSSION

This study will inform on the feasibility of the treatment regimen using high-dose rifampicin with a shortened and individualized treatment duration for pulmonary TB.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04485156 . Registered on July 24, 2020.

Clinical standards for the dosing and management of TB drugs

BACKGROUND: Optimal drug dosing is important to ensure adequate response to treatment, prevent development of drug resistance and reduce drug toxicity. The aim of these clinical standards is to provide guidance on 'best practice´ for dosing and management of TB drugs.METHODS: A panel of 57 global experts in the fields of microbiology, pharmacology and TB care were identified; 51 participated in a Delphi process. A 5-point Likert scale was used to score draft standards. The final document represents the broad consensus and was approved by all participants.RESULTS: Six clinical standards were defined: Standard 1, defining the most appropriate initial dose for TB treatment; Standard 2, identifying patients who may be at risk of sub-optimal drug exposure; Standard 3, identifying patients at risk of developing drug-related toxicity and how best to manage this risk; Standard 4, identifying patients who can benefit from therapeutic drug monitoring (TDM); Standard 5, highlighting education and counselling that should be provided to people initiating TB treatment; and Standard 6, providing essential education for healthcare professionals. In addition, consensus research priorities were identified.CONCLUSION: This is the first consensus-based Clinical Standards for the dosing and management of TB drugs to guide clinicians and programme managers in planning and implementation of locally appropriate measures for optimal person-centred treatment to improve patient care.

High intrapulmonary rifampicin and isoniazid concentrations are associated with rapid sputum bacillary clearance in patients with pulmonary tuberculosis

Background

Intrapulmonary pharmacokinetics may better explain response to tuberculosis (TB) treatment than plasma pharmacokinetics. We explored these relationships by modeling bacillary clearance in sputum in adult patients on first-line treatment in Malawi.

Methods

Bacillary elimination rates (BER) were estimated using linear mixed-effects modelling of serial time-to-positivity in mycobacterial growth indicator tubes for sputum collected during the intensive phase of treatment (weeks 0–8) for microbiologically confirmed TB. Population pharmacokinetic models used plasma and intrapulmonary drug levels at 8 and 16 weeks. Pharmacokinetic-pharmacodynamic relationships were investigated using individual-level measures of drug exposure (area-under-the-concentration-time-curve [AUC] and C_max) for rifampicin, isoniazid, pyrazinamide, and ethambutol, in plasma, epithelial lining fluid, and alveolar cells as covariates in the bacillary elimination models.

Results

Among 157 participants (58% human immunodeficiency virus [HIV] coinfected), drug exposure in plasma or alveolar cells was not associated with sputum bacillary clearance. Higher peak concentrations (C_max) or exposure (AUC) to rifampicin or isoniazid in epithelial lining fluid was associated with more rapid bacillary elimination and shorter time to sputum negativity. More extensive disease on baseline chest radiograph was associated with slower bacillary elimination. Clinical outcome was captured in 133 participants, with 15 (11%) unfavorable outcomes recorded (recurrent TB, failed treatment, or death). No relationship between BER and late clinical outcome was identified.

Conclusions

Greater intrapulmonary drug exposure to rifampicin or isoniazid in the epithelial lining fluid was associated with more rapid bacillary clearance. Higher doses of rifampicin and isoniazid may result in sustained high intrapulmonary drug exposure, rapid bacillary clearance, shorter treatment duration and better treatment outcomes.

Emerging data on rifampicin pharmacokinetics and approaches to optimal dosing in children with tuberculosis

INTRODUCTION

Despite its longstanding role in tuberculosis (TB) treatment, there continues to be emerging rifampicin research that has important implications for pediatric TB treatment and outstanding questions about its pharmacokinetics and optimal dose in children.

AREAS COVERED

This review aims to summarize and discuss emerging data on the use of rifampicin for: 1) routine treatment of drug-susceptible TB; 2) special subpopulations such as children with malnutrition, HIV, or TB meningitis; 3) treatment shortening. We also highlight the implications of these new data for child-friendly rifampicin formulations and identify future research priorities.

EXPERT OPINION

New data consistently show low rifampicin exposures across all pediatric populations with 10-20 mg/kg dosing. Although clinical outcomes in children are generally good, rifampicin dose optimization is needed, especially given a continued push to shorten treatment durations and for specific high-risk populations of children who have worse outcomes. A pooled analysis of existing data using applied pharmacometrics would answer many of the important questions remaining about rifampicin pharmacokinetics needed to optimize doses, especially in special populations. Targeted clinical studies in children with TB meningitis and treatment shortening with high-dose rifampicin are also priorities.

Safety and pharmacokinetics-pharmacodynamics of a shorter tuberculosis treatment with high-dose pyrazinamide and rifampicin: a study protocol of a phase II clinical trial (HighShort-RP)

INTRODUCTION

Increased dosing of rifampicin and pyrazinamide seems a viable strategy to shorten treatment and prevent relapse of drug-susceptible tuberculosis (TB), but safety and efficacy remains to be confirmed. This clinical trial aims to explore safety and pharmacokinetics-pharmacodynamics of a high-dose pyrazinamide-rifampicin regimen.

METHODS AND ANALYSIS

Adult patients with pulmonary TB admitted to six hospitals in Sweden and subjected to receive first-line treatment are included. Patients are randomised (1:3) to either 6-month standardised TB treatment or a 4-month regimen based on high-dose pyrazinamide (40 mg/kg) and rifampicin (35 mg/kg) along with standard doses of isoniazid and ethambutol. Plasma samples for measurement of drug exposure determined by liquid chromatography tandem-mass spectrometry are obtained at 0, 1, 2, 4, 6, 8, 12 and 24 hours, at day 1 and 14. Maximal drug concentration (Cmax) and area under the concentration-time curve (AUC0-24h) are estimated by non-compartmental analysis. Conditions for early model-informed precision dosing of high-dose pyrazinamide-rifampicin are pharmacometrically explored. Adverse drug effects are monitored throughout the study and graded according to Common Terminology Criteria for Adverse Events V.5.0. Early bactericidal activity is assessed by time to positivity in BACTEC MGIT 960 of induced sputum collected at day 0, 5, 8, 15 and week 8. Minimum inhibitory concentrations of first-line drugs are determined using broth microdilution. Disease severity is assessed with X-ray grading and a validated clinical scoring tool (TBscore II). Clinical outcome is registered according to WHO definitions (2020) in addition to occurrence of relapse after end of treatment. Primary endpoint is pyrazinamide AUC0-24h and main secondary endpoint is safety.

ETHICS AND DISSEMINATION

The study is approved by the Swedish Ethical Review Authority and the Swedish Medical Products Agency. Informed written consent is collected before study enrolment. The study results will be submitted to a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NCT04694586.

Genetic Variants and Drug Efficacy in Tuberculosis: A Step toward Personalized Therapy

Tuberculosis (TB) continues to be a major infectious disease affecting individuals worldwide. Current TB treatment strategy recommends the standard short-course chemotherapy regimen containing first-line drug, i.e., isoniazid, rifampicin, pyrazinamide, and ethambutol to treat patients suffering from drug-susceptible TB. Although Mycobacterium tuberculosis, the causing agent, is susceptible to drugs, some patients do not respond to the treatment or treatment may result in serious adverse reactions. Many studies revealed that anti-TB drug-related toxicity is associated with genetic variations, and these variations may also influence attaining maximum drug concentration. Thus, inter-individual diversities play a characteristic role by influencing the genes involved in drug metabolism pathways. The development of pharmacogenomics could bring a revolution in the field of treatment, and the understanding of germline variants may give rise to optimized targeted treatments and refine the response to standard therapy. In this review, we briefly introduced the field of pharmacogenomics with the evolution in genetics and discussed the pharmacogenetic impact of genetic variations on genes involved in the activities, such as anti-TB drug transportation, metabolism, and gene regulation.

Pharmacokinetics and safety of high-dose rifampicin in children with TB: the Opti-Rif trial

BACKGROUND

Rifampicin doses of 40 mg/kg in adults are safe and well tolerated, may shorten anti-TB treatment and improve outcomes, but have not been evaluated in children.

OBJECTIVES

To characterize the pharmacokinetics and safety of high rifampicin doses in children with drug-susceptible TB.

PATIENTS AND METHODS

The Opti-Rif trial enrolled dosing cohorts of 20 children aged 0-12 years, with incremental dose escalation with each subsequent cohort, until achievement of target exposures or safety concerns. Cohort 1 opened with a rifampicin dose of 15 mg/kg for 14 days, with a single higher dose (35 mg/kg) on day 15. Pharmacokinetic data from days 14 and 15 were analysed using population modelling and safety data reviewed. Incrementally increased rifampicin doses for the next cohort (days 1-14 and day 15) were simulated from the updated model, up to the dose expected to achieve the target exposure [235 mg/L·h, the geometric mean area under the concentration-time curve from 0 to 24 h (AUC0-24) among adults receiving a 35 mg/kg dose].

RESULTS

Sixty-two children were enrolled in three cohorts. The median age overall was 2.1 years (range = 0.4-11.7). Evaluated doses were ∼35 mg/kg (days 1-14) and ∼50 mg/kg (day 15) for cohort 2 and ∼60 mg/kg (days 1-14) and ∼75 mg/kg (day 15) for cohort 3. Approximately half of participants had an adverse event related to study rifampicin; none was grade 3 or higher. A 65-70 mg/kg rifampicin dose was needed in children to reach the target exposure.

CONCLUSIONS

High rifampicin doses in children achieved target exposures and the doses evaluated were safe over 2 weeks.

Pharmacokinetics of first-line drugs in children with tuberculosis using WHO-recommended weight band doses and formulations

Background

Dispersible pediatric fixed-dose combination (FDC) tablets delivering higher doses of first-line antituberculosis drugs in World Health Organization–recommended weight bands were introduced in 2015. We report the first pharmacokinetic data for these FDC tablets in Zambian and South African children in the treatment-shortening SHINE trial.

Methods

Children weighing 4.0–7.9, 8.0–11.9, 12.0–15.9, or 16.0–24.9 kg received 1, 2, 3, or 4 tablets daily, respectively (rifampicin/isoniazid/pyrazinamide [75/50/150 mg], with or without 100 mg ethambutol, or rifampicin/isoniazid [75/50 mg]). Children 25.0–36.9 kg received doses recommended for adults <37 kg (300, 150, 800, and 550 mg/d, respectively, for rifampicin, isoniazid, pyrazinamide, and ethambutol). Pharmacokinetics were evaluated after at least 2 weeks of treatment.

Results

In the 77 children evaluated, the median age (interquartile range) was 3.7 (1.4–6.6) years; 40 (52%) were male and 20 (26%) were human immunodeficiency virus positive. The median area under the concentration-time curve from 0 to 24 hours for rifampicin, isoniazid, pyrazinamide, and ethambutol was 32.5 (interquartile range, 20.1–45.1), 16.7 (9.2–25.9), 317 (263–399), and 9.5 (7.5–11.5) mg⋅h/L, respectively, and lower in children than in adults for rifampicin in the 4.0–7.9-, 8–11.9-, and ≥25-kg weight bands, isoniazid in the 4.0–7.9-kg and ≥25-kg weight bands, and ethambutol in all 5 weight bands. Pyrazinamide exposures were similar to those in adults.

Conclusions

Recommended weight band–based FDC doses result in lower drug exposures in children in lower weight bands and in those ≥25 kg (receiving adult doses). Further adjustments to current doses are needed to match current target exposures in adults. The use of ethambutol at the current World Health Organization–recommended doses requires further evaluation.

Pharmacokinetics and Target Attainment of SQ109 in Plasma and Human-Like Tuberculosis Lesions in Rabbits

SQ109 is a novel well-tolerated drug candidate in clinical development for the treatment of drug-resistant tuberculosis (TB). It is the only inhibitor of the MmpL3 mycolic acid transporter in clinical development. No SQ109-resistant mutant has been directly isolated thus far in vitro, in mice, or in patients, which is tentatively attributed to its multiple targets. It is considered a potential replacement for poorly tolerated components of multidrug-resistant TB regimens. To prioritize SQ109-containing combinations with the best potential for cure and treatment shortening, one must understand its contribution against different bacterial populations in pulmonary lesions. Here, we have characterized the pharmacokinetics of SQ109 in the rabbit model of active TB and its penetration at the sites of disease—lung tissue, cellular and necrotic lesions, and caseum. A two-compartment model with first-order absorption and elimination described the plasma pharmacokinetics. At the human-equivalent dose, parameter estimates fell within the ranges published for preclinical species. Tissue concentrations were modeled using an “effect” compartment, showing high accumulation in lung and cellular lesion areas with penetration coefficients in excess of 1,000 and lower passive diffusion in caseum after 7 daily doses. These results, together with the hydrophobic nature and high nonspecific caseum binding of SQ109, suggest that multiweek dosing would be required to reach steady state in caseum and poorly vascularized compartments, similar to bedaquiline. Linking lesion pharmacokinetics to SQ109 potency in assays against replicating, nonreplicating, and intracellular M. tuberculosis showed SQ109 concentrations markedly above pharmacokinetic-pharmacodynamic targets in lung and cellular lesions throughout the dosing interval.

Effect of efavirenz-based ART on the pharmacokinetics of rifampicin and its primary metabolite in patients coinfected with TB and HIV

Objectives

To evaluate the effects of concomitant efavirenz-based ART and genetic polymorphism on the variability in rifampicin and 25-desacetylrifampicin pharmacokinetics.

Patients and methods

Plasma concentrations of rifampicin and 25-desacetylrifampicin from 63 patients coinfected with TB and HIV were analysed by LC-MS/MS followed by non-linear mixed-effects modelling. Patients were genotyped for SLCO1B1 (463 C>A, 388 A>G, 11187 G>A, rs4149015, 521 T>C and 1436 G>C) and SLCO1B3 (334 T>G).

Results

One-compartment disposition models described the observations adequately. The oral clearances of rifampicin and 25-desacetylrifampicin were 140% and 110% higher, respectively, in patients on concomitant efavirenz-based ART. Rifampicin bioavailability was also lower in patients on concomitant ART. Further, although not included in the final model, a lower relative bioavailability in carriers of WT SLCO1B3 334 T>G compared with carriers of mutations in the genotype was estimated.

Conclusions

The results presented indicate both pre-systemic and systemic induction by efavirenz-based ART affecting rifampicin pharmacokinetics. The described drug–drug interaction has a clinical impact on rifampicin exposure prior to steady state and may impact the early bactericidal activity in patients on efavirenz-based ART.

Treatment effect measures for culture conversion endpoints in phase IIb tuberculosis treatment trials

Phase IIb trials of tuberculosis therapy rely on early biomarkers of treatment effect. Despite limited predictive ability for clinical outcomes, culture conversion, the event in which an individual previously culture positive for Mycobacterium tuberculosis yields a negative culture after initiating treatment, is a commonly used endpoint. Lack of consensus on how to define the outcome and corresponding measure of treatment effect complicates interpretation and limits between-trial comparisons. We review common analytic approaches to measuring treatment effect and introduce difference in restricted mean survival times as an alternative to identify faster times to culture conversion and express magnitude of effect on the time scale. Findings from the PanACEA MAMSTB trial are reanalyzed as an illustrative example. In a systematic review we demonstrate variability in analytic approaches, sampling strategies, and outcome definitions in phase IIb tuberculosis trials. Harmonization would allow for larger meta-analyses, and may help expedite advancement of new TB therapeutics.

Increased bactericidal activity but dose-limiting intolerability at 50 mg·kg-1 rifampicin

Background

Accumulating data indicate that higher rifampicin doses are more effective and shorten tuberculosis (TB) treatment duration. This study evaluated the safety, tolerability, pharmacokinetics, and 7- and 14-day early bactericidal activity (EBA) of increasing doses of rifampicin. Here we report the results of the final cohorts of PanACEA HIGHRIF1, a dose escalation study in treatment-naive adult smear-positive patients with TB.

Methods

Patients received, in consecutive cohorts, 40 or 50 mg·kg⁻¹ rifampicin once daily in monotherapy (day 1–7), supplemented with standard dose isoniazid, pyrazinamide and ethambutol between days 8 and 14.

Results

In the 40 mg·kg⁻¹ cohort (n=15), 13 patients experienced a total of 36 adverse events during monotherapy, resulting in one treatment discontinuation. In the 50 mg·kg⁻¹ cohort (n=17), all patients experienced adverse events during monotherapy, 93 in total; 11 patients withdrew or stopped study medication. Adverse events were mostly mild/moderate and tolerability rather than safety related, i.e. gastrointestinal disorders, pruritis, hyperbilirubinaemia and jaundice. There was a more than proportional increase in the rifampicin geometric mean area under the plasma concentration–time curve from time 0 to 12 h (AUC_0–24 h) for 50 mg·kg⁻¹ compared with 40 mg·kg⁻¹; 571 (range 320–995) versus 387 (range 201–847) mg·L⁻¹·h, while peak exposures saw proportional increases. Protein-unbound exposure after 50 mg·kg⁻¹ (11% (range 8–17%)) was comparable with lower rifampicin doses. Rifampicin exposures and bilirubin concentrations were correlated (Spearman's ρ=0.670 on day 3, p<0.001). EBA increased considerably with dose, with the highest seen after 50 mg·kg⁻¹: 14-day EBA −0.427 (95% CI −0.500– −0.355) log₁₀CFU·mL⁻¹·day⁻¹.

Conclusion

Although associated with an increased bactericidal effect, the 50 mg·kg⁻¹ dose was not well tolerated. Rifampicin at 40 mg·kg⁻¹ was well tolerated and therefore selected for evaluation in a phase IIc treatment-shortening trial.

While bactericidal activity continues to increase with dose, for the first time we identified dose-limiting intolerability for rifampicin dosed at 50 mg·kg⁻¹; 40 mg·kg⁻¹ seems the optimal tolerable dose for evaluation in TB treatment-shortening trialshttps://bit.ly/37dUIuB

Standard versus high dose of rifampicin in the treatment of pulmonary tuberculosis: a systematic review and meta-analysis

OBJECTIVES

A growing amount of evidence suggests that the rifampicin dosing currently recommended for tuberculosis treatment could be associated with inadequate exposure and unfavourable outcomes. We aimed to compare clinical and microbiological efficacy and safety outcomes of standard and higher rifampicin dosing.

METHODS

Data sources were MEDLINE, Google Scholar and the Cochrane Library. This was a systematic review and meta-analysis that included experimental or observational studies comparing 8-week sputum culture conversion, treatment failure, or safety outcomes in naïve patients with pulmonary tuberculosis treated with standard (10 mg/kg) or higher doses of rifampicin.

RESULTS

Of a total of 9683 citations screened, eight randomized controlled trials were included, accounting for 1897 subjects; the risk of bias was low in three studies, high in two and intermediate in three. At week 8 a higher proportion of patients in the high-dose group obtained a sputum culture conversion than those in the standard dose group (83.7% versus 80.6%, RR 1.06; 95%CI 1.01-1.12, p 0.028); this result was confirmed in the sub-analysis including patients treated with a rifampicin dose of ≥20 mg/kg, but not in those treated with 11-19 mg/kg. Events of treatment failure at end of treatment showed no significant difference between the two groups (RR 0.84; 95%CI 0.59-1.21, p 0.362). In the analysis evaluating safety outcome, the difference in the occurrence of a grade 3 or 4 liver toxicity or adverse drug reactions leading to discontinuation was not significant at the statistical analysis among the groups (7.2% versus 5.4%, RR 1.19; 95%CI 0.81-1.73, p 0.370, and 1.5% versus 0.6%, RR 2.31; 95%CI 0.65-8.21, p 0.195, respectively). No statistical heterogeneity among studies was observed for each outcome.

CONCLUSIONS

High doses of rifampicin were associated with an increased rate of sputum culture conversion at 8 weeks of treatment, particularly in patients receiving ≥20 mg/kg.

Four-Month Rifapentine Regimens with or without Moxifloxacin for Tuberculosis

BACKGROUND

Rifapentine-based regimens have potent antimycobacterial activity that may allow for a shorter course in patients with drug-susceptible pulmonary tuberculosis.

METHODS

In an open-label, phase 3, randomized, controlled trial involving persons with newly diagnosed pulmonary tuberculosis from 13 countries, we compared two 4-month rifapentine-based regimens with a standard 6-month regimen consisting of rifampin, isoniazid, pyrazinamide, and ethambutol (control) using a noninferiority margin of 6.6 percentage points. In one 4-month regimen, rifampin was replaced with rifapentine; in the other, rifampin was replaced with rifapentine and ethambutol with moxifloxacin. The primary efficacy outcome was survival free of tuberculosis at 12 months.

RESULTS

Among 2516 participants who had undergone randomization, 2343 had a culture positive for Mycobacterium tuberculosis that was not resistant to isoniazid, rifampin, or fluoroquinolones (microbiologically eligible population; 768 in the control group, 791 in the rifapentine-moxifloxacin group, and 784 in the rifapentine group), of whom 194 were coinfected with human immunodeficiency virus and 1703 had cavitation on chest radiography. A total of 2234 participants could be assessed for the primary outcome (assessable population; 726 in the control group, 756 in the rifapentine-moxifloxacin group, and 752 in the rifapentine group). Rifapentine with moxifloxacin was noninferior to the control in the microbiologically eligible population (15.5% vs. 14.6% had an unfavorable outcome; difference, 1.0 percentage point; 95% confidence interval [CI], -2.6 to 4.5) and in the assessable population (11.6% vs. 9.6%; difference, 2.0 percentage points; 95% CI, -1.1 to 5.1). Noninferiority was shown in the secondary and sensitivity analyses. Rifapentine without moxifloxacin was not shown to be noninferior to the control in either population (17.7% vs. 14.6% with an unfavorable outcome in the microbiologically eligible population; difference, 3.0 percentage points [95% CI, -0.6 to 6.6]; and 14.2% vs. 9.6% in the assessable population; difference, 4.4 percentage points [95% CI, 1.2 to 7.7]). Adverse events of grade 3 or higher occurred during the on-treatment period in 19.3% of participants in the control group, 18.8% in the rifapentine-moxifloxacin group, and 14.3% in the rifapentine group.

CONCLUSIONS

The efficacy of a 4-month rifapentine-based regimen containing moxifloxacin was noninferior to the standard 6-month regimen in the treatment of tuberculosis. (Funded by the Centers for Disease Control and Prevention and others; Study 31/A5349 ClinicalTrials.gov number, NCT02410772.).

Rifampicin Can Be Given as Flat-Dosing Instead of Weight-Band Dosing

BACKGROUND

The weight-band dosing in tuberculosis treatment regimen has been implemented in clinical practice for decades. Patients will receive different number of fixed dose combination tablets according to their weight-band. However, some analysis has shown that weight was not the best covariate to explain variability of rifampicin exposure. Furthermore, the rationale for using weight-band dosing instead of flat-dosing becomes questionable. Therefore, this study aimed to compare the average and the variability of rifampicin exposure after weight-band dosing and flat-dosing.

METHODS

Rifampicin exposure were simulated using previously published population pharmacokinetics model at dose 10-40 mg/kg for weight-band dosing and dose 600-2400 mg for flat-dosing. The median area under the curve (AUC0-24 h) after day 7 and 14 were compared as well as the variability of each dose group between weight-band and flat-dosing.

RESULTS

The difference of median AUC0-24 h of all dose groups between flat-dosing and weight-band dosing were considered low (< 20%) except for the lowest dose. At the dose of 10 mg/kg (600 mg for flat-dosing), flat-dosing resulted in higher median AUC0-24h compared to the weight-band dosing. A marginal decrease in between-patient variability was predicted for weight-band dosing compared to flat-dosing.

CONCLUSIONS

Weight-band dosing yields a small and non-clinically relevant decrease in variability of AUC0-24h.

The Treatment of Tuberculosis

Tuberculosis (TB) remains a leading cause of infectious death worldwide, and poverty is a major driver. Clinically, TB presents as "latent" TB and active TB disease, and the treatment for each is different. TB drugs can display "early bactericidal activity (EBA)" and / or "sterilizing activity" (clearing persisters). Isoniazid is excellent at the former, and rifampin is excellent at the latter. Pyrazinamide and ethambutol complete the first-line regimen for drug-susceptible TB, each playing a specific role. Drug-resistant TB is an increasing concern, being met, in part, with repurposed drugs (including moxifloxacin, levofloxacin, linezolid, clofazimine, and beta-lactams) and new drugs (including bedaquiline, pretomanid, and delamanid). One challenge is to select drugs without overlapping adverse drug reaction profiles. QTc interval prolongation is one such concern, but to date, it has been manageable. Drug penetration into organism sanctuaries, such as the central nervous system, bone, and pulmonary TB cavities remain important challenges. The pharmacodynamics of most TB drugs can be described by the area under the curve (AUC) divided by the minimal inhibitory concentration (MIC). The hollow fiber infection model (HFIM) and various animal models (especially mouse and macaque) allow for sophisticated pharmacokinetic/pharmacodynamic experiments. These experiments may hasten the selection of the most potent, shortest possible regimens to treat even extremely drug resistant TB. These findings can be translated to humans by optimizing drug exposure in each patient, using therapeutic drug monitoring and dose individualization.

Higher Dosing of Rifamycins Does Not Increase Activity against Mycobacterium tuberculosis in the Hollow-Fiber Infection Model

Improvements in the translational value of preclinical models can allow more-successful and more-focused research on shortening the duration of tuberculosis treatment. Although the hollow-fiber infection model (HFIM) is considered a valuable addition to the drug development pipeline, its exact role has not been fully determined yet. Since the strategy of increasing the dose of rifamycins is being evaluated for its treatment-shortening potential, additional in vitro modeling is important. Therefore, we assessed increased dosing of rifampin and rifapentine in our HFIM in order to gain more insight into the place of the HFIM in the drug development pipeline. Total and free-fraction concentrations corresponding to daily dosing of 2.7, 10, and 50 mg of rifampin/kg of body weight, as well as 600 mg and 1,500 mg rifapentine, were assessed in our HFIM using the Mycobacterium tuberculosis H37Rv strain. Drug activity and the emergence of drug resistance were assessed by CFU counting and subsequent mathematical modeling over 14 days, and pharmacokinetic exposures were checked. We found that increasing rifampin exposure above what is expected with the standard dose did not result in higher antimycobacterial activity. For rifapentine, only the highest concentration showed increased activity, but the clinical relevance of this observation is questionable. Moreover, for both drugs, the emergence of resistance was unrelated to exposure. In conclusion, in the simplest experimental setup, the results of the HFIM did not fully correspond to preexisting clinical data. The inclusion of additional parameters and readouts in this preclinical model could be of interest for proper assessment of the translational value of the HFIM.

High-Dose Oral and Intravenous Rifampicin for the Treatment of Tuberculous Meningitis in Predominantly Human Immunodeficiency Virus (HIV)-Positive Ugandan Adults: A Phase II Open-Label Randomized Controlled Trial

BACKGROUND

High-dose rifampicin may improve outcomes of tuberculous meningitis (TBM). Little safety or pharmacokinetic (PK) data exist on high-dose rifampicin in human immunodeficiency virus (HIV) coinfection, and no cerebrospinal fluid (CSF) PK data exist from Africa. We hypothesized that high-dose rifampicin would increase serum and CSF concentrations without excess toxicity.

METHODS

In this phase II open-label trial, Ugandan adults with suspected TBM were randomized to standard-of-care control (PO-10, rifampicin 10 mg/kg/day), intravenous rifampicin (IV-20, 20 mg/kg/day), or high-dose oral rifampicin (PO-35, 35 mg/kg/day). We performed PK sampling on days 2 and 14. The primary outcomes were total exposure (AUC0-24), maximum concentration (Cmax), CSF concentration, and grade 3-5 adverse events.

RESULTS

We enrolled 61 adults, 92% were living with HIV, median CD4 count was 50 cells/µL (interquartile range [IQR] 46-56). On day 2, geometric mean plasma AUC0-24hr was 42.9·h mg/L with standard-of-care 10 mg/kg dosing, 249·h mg/L for IV-20 and 327·h mg/L for PO-35 (P < .001). In CSF, standard of care achieved undetectable rifampicin concentration in 56% of participants and geometric mean AUC0-24hr 0.27 mg/L, compared with 1.74 mg/L (95% confidence interval [CI] 1.2-2.5) for IV-20 and 2.17 mg/L (1.6-2.9) for PO-35 regimens (P < .001). Achieving CSF concentrations above rifampicin minimal inhibitory concentration (MIC) occurred in 11% (2/18) of standard-of-care, 93% (14/15) of IV-20, and 95% (18/19) of PO-35 participants. Higher serum and CSF levels were sustained at day 14. Adverse events did not differ by dose (P = .34).

CONCLUSIONS

Current international guidelines result in sub-therapeutic CSF rifampicin concentration for 89% of Ugandan TBM patients. High-dose intravenous and oral rifampicin were safe and respectively resulted in exposures ~6- and ~8-fold higher than standard of care, and CSF levels above the MIC.

Population Pharmacokinetics and Bayesian Dose Adjustment to Advance TDM of Anti-TB Drugs

Tuberculosis (TB) is still the number one cause of death due to an infectious disease. Pharmacokinetics and pharmacodynamics of anti-TB drugs are key in the optimization of TB treatment and help to prevent slow response to treatment, acquired drug resistance, and adverse drug effects. The aim of this review was to provide an update on the pharmacokinetics and pharmacodynamics of anti-TB drugs and to show how population pharmacokinetics and Bayesian dose adjustment can be used to optimize treatment. We cover aspects on preclinical, clinical, and population pharmacokinetics of different drugs used for drug-susceptible TB and multidrug-resistant TB. Moreover, we include available data to support therapeutic drug monitoring of these drugs and known pharmacokinetic and pharmacodynamic targets that can be used for optimization of therapy. We have identified a wide range of population pharmacokinetic models for first- and second-line drugs used for TB, which included models built on NONMEM, Pmetrics, ADAPT, MWPharm, Monolix, Phoenix, and NPEM2 software. The first population models were built for isoniazid and rifampicin; however, in recent years, more data have emerged for both new anti-TB drugs, but also for defining targets of older anti-TB drugs. Since the introduction of therapeutic drug monitoring for TB over 3 decades ago, further development of therapeutic drug monitoring in TB next steps will again depend on academic and clinical initiatives. We recommend close collaboration between researchers and the World Health Organization to provide important guideline updates regarding therapeutic drug monitoring and pharmacokinetics/pharmacodynamics.

Rifampicin and Isoniazid Maximal Concentrations are Below Efficacy-associated Thresholds in the Majority of Patients: Time to Increase the Doses?

BACKGROUND

The treatment of drug-sensitive tuberculosis (TB) is highly effective; however, many patients have suboptimal drug exposure, which possibly explains treatment failures and selection of resistance. This study aimed to describe the prevalence and determinants of suboptimal maximal concentrations (C_max) for anti-TB drugs.

METHODS

An observational study was conducted in patients receiving first-line anti-TB treatment. At two early time points (T1 and T2), blood samples were withdrawn 2 hours post-dose (C_max) and drug concentrations were measured. Data were expressed as medians (interquartile ranges).

RESULTS

The study included 199 participants: 72.9% were male and the median age was 39.8 years (27.5-51.4). The median C_max at T1 and T2 were 7950 ng/mL and 7122 ng/mL (rifampicin), 3260 ng/mL and 3185 ng/mL (isoniazid), 4210 ng/mL and 5742 ng/mL (ethambutol), and 31 008 ng/mL and 30 352 ng/mL (pyrazinamide), respectively. Higher doses/kg and other variables (being born in Italy and female gender for rifampicin, older age and proton pump inhibitor use for isoniazid, female gender and older age for pyrazinamide) were identified by multivariate linear regression analysis. Participants with a higher body mass index received lower doses/kg of all anti-TB drugs. Suboptimal C_max at T1 and T2 were observed in 60% and 66% (rifampicin), 54% and 55% (isoniazid), 33% and 39% (ethambutol), 20% and 11% (pyrazinamide) of patients. Despite 21% of patients at T1 and 24% at T2 showing two or more drugs with suboptimal exposure, no effect on treatment outcome was observed.

DISCUSSION

The majority of patients receiving first-line anti-TB drugs had low isoniazid and rifampin C_max. Increased doses or the use of therapeutic drug monitoring in selected patients may be advised.

Shortened Tuberculosis Treatment for People with HIV in South Africa. A Model-based Evaluation and Cost-effectiveness Analysis

Rationale: Recent tuberculosis treatment trials failed to show that some 4-month (4m) regimens were noninferior to conventional 6-month (6m) regimens for a composite clinical outcome. Novel shortened regimens may still have important clinical and economic benefits in populations with high loss to follow-up (LTFU) and in subgroups such as people with human immunodeficiency virus.Objectives: To identify scenarios in which a novel 4m regimen would be preferred to a conventional 6m regimen for treatment of drug-susceptible tuberculosis in people with human immunodeficiency virus in South Africa, in terms of short-term and long-term clinical and economic outcomes.Methods: We used the Cost-Effectiveness of Preventing AIDS Complications-International microsimulation model to project outcomes modeled on participants in the OFLOTUB trial. For calibration purposes, we did a base case analysis by applying trial-informed parameters for the 4m/6m regimens, including monthly LTFU during treatment (0.68%/0.83%), average monthly tuberculosis recurrence (0.65%/0.31%), and monthly drug costs (U.S. dollars [USD]25.90/3.70). We then evaluated different scenarios and 4m regimen characteristics, varying key parameters, including LTFU (informed by observational cohort data), recurrence, and cost. We projected outcomes, including 2-year mortality and life expectancy. We conducted a cost-effectiveness analysis, evaluating the incremental cost-effectiveness ratio of a 4m versus 6m regimen.Results: In the base case model analysis, risk of the composite unfavorable outcome in the 4m/6m groups was 19.8%/15.9%, similar to the trial; projected life expectancies were 22.1/22.3 years. In analyses of alternative scenarios and 4m regimen characteristics, a 4m regimen yielded lower risk of the composite unfavorable outcome than the conventional 6m regimen if LTFU increased to greater than 3.5%/mo or if average recurrence after a 4m regimen decreased to less than 0.45%/mo, and it yielded higher life expectancy if LTFU was greater than 3.5%/mo or if recurrence was less than 0.5%/mo. A 4m regimen was not cost-effective in the base case but became cost-effective (incremental cost-effectiveness ratio <USD940/yr of life saved) in two-way sensitivity analysis; for example, if LTFU was greater than or equal to 5.3%/mo and either average recurrence was less than or equal to 0.5%/mo or drug cost was less than or equal to USD15/mo.Conclusions: A novel shortened tuberculosis treatment regimen could improve outcomes such as survival despite conferring a higher recurrence risk, particularly in settings where LTFU is higher than that seen in recent trials.

The Impact of First-Line Anti-Tubercular Drugs' Pharmacokinetics on Treatment Outcome: A Systematic Review

BACKGROUND

Tuberculosis remains the major public health problem besides tremendous efforts to combat it. Most tuberculosis patients are treated with a standard dose of first-line anti-TB drugs. The cure rate, however, varies from patient to patient. Various factors have been related to anti-TB treatment failure. In recent years, studies associating lower plasma concentrations of anti-TB drugs with poor treatment outcomes are emerging although the results are inconclusive.

OBJECTIVE

Investigate the impact of first-line anti-tubercular drugs pharmacokinetics on treatment outcome.

METHODS

A systematic search of Pubmed, EMBASE, Web of Science, and the Cochrane Library for articles published in the English language between January 2010 to June 2020 was conducted to identify eligible studies describing associations of first-line anti-tubercular drug pharmacokinetics with treatment outcomes. The primary outcomes considered were pharmacokinetics parameter results and its association with treatment outcome.

RESULTS

The search identified 1754 articles of which twelve articles; ten prospective observational studies and two controlled clinical trials fulfilled the eligibility criteria. The majority of the studies showed target concentrations for the first-line anti-tubercular drugs below the current standard range. Among the twelve studies, eleven studies assessed rifampicin pharmacokinetics of which eight reported association of drug concentration and treatment outcomes. Similarly, four out of eight and three out of seven reported drug concentration and treatment outcome association for isoniazid and pyrazinamide, respectively. Despite the low plasma concentration, a favorable treatment outcome was achieved for the bulk of the patients. Irrespective of the inconsistency, an increase in exposure to rifampicin improved the outcome, and lower rifampicin, isoniazid, and pyrazinamide concentration are associated with poor outcome. No data are available for ethambutol associating its pharmacokinetics with treatment outcomes.

CONCLUSION

The pharmacokinetics of first-line antitubercular drugs can influence treatment outcomes. Further controlled clinical studies are, however, required to establish these relationships.

Time-to-Event Analysis of Paclitaxel-Associated Peripheral Neuropathy in Advanced Non-Small-Cell Lung Cancer Highlighting Key Influential Treatment/Patient Factors

Paclitaxel-associated peripheral neuropathy (PN), a major dose-limiting toxicity, significantly impacts patients' quality of life/treatment outcome. Evaluation of risk factors often ignores time of PN onset, precluding the impact of time-dependent factors, e.g., drug exposure, needed to comprehensively characterize PN. We employed parametric time-to-event (TTE) analysis to describe the time course of risk of first occurrence of clinically relevant PN grades ≥2 (PN2+, n = 105, common terminology criteria v4.0) and associated patient/treatment characteristics, leveraging data from 365 patients (1454 cycles) receiving paclitaxel every 3 weeks (plus carboplatin AUC = 6 or cisplatin 80 mg/m2) for ≤6 cycles. Paclitaxel was intravenously administered (3 hours) as standard 200-mg/m2 doses (n = 182) or as pharmacokinetic-guided dosing (n = 183). A cycle-varying hazard TTE model linking surge in hazard of PN2+ to paclitaxel administration [PN2+ proportions (i.e., cases per 1000 patients), 1st day, cycle 1: 4.87 of 1000; cycle 6: 7.36 of 1000] and linear decline across cycle (last day, cycle 1: 1.64 of 1000; cycle 6: 2.48 of 1000) adequately characterized the time-varying hazard of PN2+. From joint covariate evaluation, PN2+ proportions (1st day, cycle 1) increased by 1.00 per 1000 with 5-μmol·h/l higher paclitaxel exposure per cycle (AUC between the start and end of a cycle, most relevant covariate), 0.429 per 1000 with 5-year higher age, 1.31 per 1000 (smokers vs. nonsmokers), and decreased by 0.670 per 1000 (females vs. males). Compared to 200 mg/m2 dosing every 3 weeks, model-predicted cumulative risk of PN2+ was significantly higher (42%) with 80 mg/m2 weekly dosing but reduced by 11% with 175 mg/m2 dosing every 3 weeks. The established TTE modeling framework enables quantification and comparison of patient's cumulative risks of PN2+ for different clinically relevant paclitaxel dosing schedules, sparing patients PN2+ to improve paclitaxel therapy. SIGNIFICANCE STATEMENT: Characterization of risk factors of paclitaxel-associated peripheral neuropathy (PN) typically involves time-independent comparison of PN odds in patient subpopulations, concealing the impact of time-dependent factors, e.g., changing paclitaxel exposure, required to comprehensively characterize PN. We developed a parametric time-to-event model describing the time course in risk of clinically relevant paclitaxel-associated PN, identifying the highest risk in older male smokers with higher paclitaxel area under the plasma concentration-time curve between the start and end of a cycle. The developed framework enabled quantification of patient's risk of PN for clinically relevant paclitaxel dosing schedules, facilitating future dosing decisions.

Model-Based Meta-analysis of Rifampicin Exposure and Mortality in Indonesian Tuberculous Meningitis Trials

BACKGROUND

Intensified antimicrobial treatment with higher rifampicin doses may improve outcome of tuberculous meningitis, but the desirable exposure and necessary dose are unknown. Our objective was to characterize the relationship between rifampicin exposures and mortality in order to identify optimal dosing for tuberculous meningitis.

METHODS

An individual patient meta-analysis was performed on data from 3 Indonesian randomized controlled phase 2 trials comparing oral rifampicin 450 mg (~10 mg/kg) to intensified regimens including 750-1350 mg orally, or a 600-mg intravenous infusion. Pharmacokinetic data from plasma and cerebrospinal fluid (CSF) were analyzed with nonlinear mixed-effects modeling. Six-month survival was described with parametric time-to-event models.

RESULTS

Pharmacokinetic analyses included 133 individuals (1150 concentration measurements, 170 from CSF). The final model featured 2 disposition compartments, saturable clearance, and autoinduction. Rifampicin CSF concentrations were described by a partition coefficient (5.5%; 95% confidence interval [CI], 4.5%-6.4%) and half-life for distribution plasma to CSF (2.1 hours; 95% CI, 1.3-2.9 hours). Higher CSF protein concentration increased the partition coefficient. Survival of 148 individuals (58 died, 15 dropouts) was well described by an exponentially declining hazard, with lower age, higher baseline Glasgow Coma Scale score, and higher individual rifampicin plasma exposure reducing the hazard. Simulations predicted an increase in 6-month survival from approximately 50% to approximately 70% upon increasing the oral rifampicin dose from 10 to 30 mg/kg, and predicted that even higher doses would further improve survival.

CONCLUSIONS

Higher rifampicin exposure substantially decreased the risk of death, and the maximal effect was not reached within the studied range. We suggest a rifampicin dose of at least 30 mg/kg to be investigated in phase 3 clinical trials.

Tuberculosis treatment in children: The changing landscape

Traditionally children have been treated for tuberculosis (TB) based on data extrapolated from adults. However, we know that children present unique challenges that deserve special focus. New data on optimal drug selection and dosing are emerging with the inclusion of children in clinical trials and ongoing research on age-related pharmacokinetics and pharmacodynamics. We discuss the changing treatment landscape for drug-susceptible and drug-resistant paediatric tuberculosis in both the most common (intrathoracic) and most severe (central nervous system) forms of disease, and address the current knowledge gaps for improving patient outcomes.

A review of recent advances in anti-tubercular drug development

Tuberculosis is a global threat but in particular affects people from developing countries. It is thought that nearly a third of the population of the world live with its causative bacteria in a dormant form. Although tuberculosis is a curable disease, the chances of cure become slim as the disease becomes multidrug-resistant and the situation gets even worse as the disease becomes extensively drug-resistant. After approximately 5 decades without any new TB drug in the pipeline, there has been some good news in the recent years with the discovery of new drugs such as bedaquiline and delamanid as well as the discovery of new classes of anti-tubercular drugs. Some old drugs such as clofazimine, linezolid and many others which were not previously indicated for tuberculosis have been also repurposed for tuberculosis and they are performing well.

Drug exposure and minimum inhibitory concentration predict pulmonary tuberculosis treatment response

BACKGROUND

Prospective studies correlating pharmacokinetic/pharmacodynamic (PK/PD) indices to clinical responses are urgently needed. This study aimed to find clinically relevant PK/PD thresholds that can be used for treatment optimization.

METHODS

Pharmacokinetic sampling and minimum inhibitory concentration (MIC) measurements were performed for culture-confirmed tuberculosis patients. Classification and regression tree (CART) analysis was applied to obtain PK and/or PD thresholds for first-line drugs predictive of two-week/month culture conversion, treatment outcome determined at 6-8 months, acute kidney injury (AKI) and drug-induced liver injury (DILI). Least absolute shrinkage and selection operator (LASSO) logistic regression was used for model development and validation.

RESULTS

Finally, 168 and 52 patients with tuberculosis were included in development and validation cohort for analysis, respectively. Area under concentration-time curve (AUC)/MIC below CART-derived thresholds for pyrazinamide of 8.42, pyrazinamide of 2.79 or rifampicin of 435.45 were the predominant predictors of two-week culture conversion, two-month culture conversion or treatment success, respectively. Isoniazid AUC above 21.78 mg·h/L or rifampicin AUC above 82.01 mg·h/L were predictive of DILI or AKI during TB treatment. The predictive performance of trained LASSO models in validation cohort was evaluated by receiver operating characteristic curves and ranged from 0.625 to 0.978.

CONCLUSIONS

PK/PD indices and drug exposure of anti-TB drugs were associated with clinical outcome and adverse events. The effect of CART-derived thresholds for individualized dosing on treatment outcome should be studied in a randomized controlled trial.

Disseminated Mycobacterium bovis Infection Complicated by Meningitis and Stroke: A Case Report

We describe a case of a 19-year-old female presenting with Mycobacterium bovis meningitis, a rarely encountered infection. We discuss the use of pyrosequencing to aid in prompt diagnosis of M. bovis infection, as well as treatment strategies and challenges given the organism’s intrinsic resistance to pyrazinamide.

Effect of diabetes mellitus on TB drug concentrations in Tanzanian patients

BACKGROUND

Diabetes mellitus (DM) is associated with poor TB treatment outcome. Previous studies examining the effect of DM on TB drug concentrations yielded conflicting results. No studies have been conducted to date in an African population.

OBJECTIVES

To compare exposure to TB drugs in Tanzanian TB patients with and without DM.

PATIENTS AND METHODS

A prospective pharmacokinetic study was performed among 20 diabetic and 20 non-diabetic Tanzanian TB patients during the intensive phase of TB treatment. Plasma pharmacokinetic parameters of isoniazid, rifampicin, pyrazinamide and ethambutol were compared using an independent-sample t-test on log-transformed data. Multiple linear regression analysis was performed to assess the effects of DM, gender, age, weight, HIV status and acetylator status on exposure to TB drugs.

RESULTS

A trend was shown for 25% lower total exposure (AUC0-24) to rifampicin among diabetics versus non-diabetics (29.9 versus 39.9 mg·h/L, P=0.052). The AUC0-24 and peak concentration (Cmax) of isoniazid were also lower in diabetic TB patients (5.4 versus 10.6 mg·h/L, P=0.015 and 1.6 versus 2.8 mg/L, P=0.013). Pyrazinamide AUC0-24 and Cmax values were non-significantly lower among diabetics (P=0.08 and 0.09). In multivariate analyses, DM remained an independent predictor of exposure to isoniazid and rifampicin, next to acetylator status for isoniazid.

CONCLUSIONS

There is a need for individualized dosing of isoniazid and rifampicin based on plasma concentration measurements (therapeutic drug monitoring) and for clinical trials on higher doses of these TB drugs in patients with TB and DM.

High dose oral rifampicin to improve survival from adult tuberculous meningitis: A randomised placebo-controlled double-blinded phase III trial (the HARVEST study)

Background: Tuberculous meningitis (TBM), the most severe form of tuberculosis (TB), results in death or neurological disability in >50%, despite World Health Organisation recommended therapy. Current TBM regimen dosages are based on data from pulmonary TB alone. Evidence from recent phase II pharmacokinetic studies suggests that high dose rifampicin (R) administered intravenously or orally enhances central nervous system penetration and may reduce TBM associated mortality. We hypothesize that, among persons with TBM, high dose oral rifampicin (35 mg/kg) for 8 weeks will improve survival compared to standard of care (10 mg/kg), without excess adverse events.

Protocol: We will perform a parallel group, randomised, placebo-controlled, double blind, phase III multicentre clinical trial comparing high dose oral rifampicin to standard of care. The trial will be conducted across five clinical sites in Uganda, South Africa and Indonesia. Participants are HIV-positive or negative adults with clinically suspected TBM, who will be randomised (1:1) to one of two arms: 35 mg/kg oral rifampicin daily for 8 weeks (in combination with standard dose isoniazid [H], pyrazinamide [Z] and ethambutol [E]) or standard of care (oral HRZE, containing 10 mg/kg/day rifampicin). The primary end-point is 6-month survival. Secondary end points are: i) 12-month survival ii) functional and neurocognitive outcomes and iii) safety and tolerability. Tertiary outcomes are: i) pharmacokinetic outcomes and ii) cost-effectiveness of the intervention. We will enrol 500 participants over 2.5 years, with follow-up continuing until 12 months post-enrolment.

Discussion: Our best TBM treatment still results in unacceptably high mortality and morbidity. Strong evidence supports the increased cerebrospinal fluid penetration of high dose rifampicin, however conclusive evidence regarding survival benefit is lacking. This study will answer the important question of whether high dose oral rifampicin conveys a survival benefit in TBM in HIV-positive and -negative individuals from Africa and Asia.

Trial registration: ISRCTN15668391 (17/06/2019)

High dose oral rifampicin to improve survival from adult tuberculous meningitis: A randomised placebo-controlled double-blinded phase III trial (the HARVEST study)

Background: Tuberculous meningitis (TBM), the most severe form of tuberculosis (TB), results in death or neurological disability in >50%, despite World Health Organisation recommended therapy. Current TBM regimen dosages are based on data from pulmonary TB alone. Evidence from recent phase II pharmacokinetic studies suggests that high dose rifampicin (R) administered intravenously or orally enhances central nervous system penetration and may reduce TBM associated mortality. We hypothesize that, among persons with TBM, high dose oral rifampicin (35 mg/kg) for 8 weeks will improve survival compared to standard of care (10 mg/kg), without excess adverse events. Protocol: We will perform a parallel group, randomised, placebo-controlled, double blind, phase III multicentre clinical trial comparing high dose oral rifampicin to standard of care. The trial will be conducted across five clinical sites in Uganda, South Africa and Indonesia. Participants are HIV-positive or negative adults with clinically suspected TBM, who will be randomised (1:1) to one of two arms: 35 mg/kg oral rifampicin daily for 8 weeks (in combination with standard dose isoniazid [H], pyrazinamide [Z] and ethambutol [E]) or standard of care (oral HRZE, containing 10 mg/kg/day rifampicin). The primary end-point is 6-month survival. Secondary end points are: i) 12-month survival ii) functional and neurocognitive outcomes and iii) safety and tolerability. Tertiary outcomes are: i) pharmacokinetic outcomes and ii) cost-effectiveness of the intervention. We will enrol 500 participants over 2.5 years, with follow-up continuing until 12 months post-enrolment. Discussion: Our best TBM treatment still results in unacceptably high mortality and morbidity. Strong evidence supports the increased cerebrospinal fluid penetration of high dose rifampicin, however conclusive evidence regarding survival benefit is lacking. This study will answer the important question of whether high dose oral rifampicin conveys a survival benefit in TBM in HIV-positive and -negative individuals from Africa and Asia. Trial registration: ISRCTN15668391 (17/06/2019).

Personalized Tuberculosis Treatment Through Model-Informed Dosing of Rifampicin

BACKGROUND AND OBJECTIVE

This study proposes a model-informed approach for therapeutic drug monitoring (TDM) of rifampicin to improve tuberculosis (TB) treatment.

METHODS

Two datasets from pulmonary TB patients were used: a pharmacokinetic study (34 patients, 373 samples), and TDM data (96 patients, 391 samples) collected at Radboud University Medical Center, The Netherlands. Nine suitable population pharmacokinetic models of rifampicin were identified in the literature and evaluated on the datasets. A model developed by Svensson et al. was found to be the most suitable based on graphical goodness of fit, residual diagnostics, and predictive performance. Prediction of individual area under the concentration-time curve from time zero to 24 h (AUC₂₄) and maximum concentration (C_max) employing various sampling strategies was compared with a previously established linear regression TDM strategy, using sampling at 2, 4, and 6 h, in terms of bias and precision (mean error [ME] and root mean square error [RMSE]).

RESULTS

A sampling strategy using 2- and 4-h blood collection was selected to be the most suitable. The bias and precision of the two strategies were comparable, except that the linear regression strategy was more biased in prediction of the AUC₂₄ than the model-informed approach (ME of 9.9% and 1.5%, respectively). A comparison of resulting dose advice, using predictions on a simulated dataset, showed no significant difference in sensitivity or specificity between the two methods. The model was successfully implemented in the InsightRX precision dosing platform.

CONCLUSION

Blood sampling at 2 and 4 h, combined with model-based prediction, can be used instead of the currently used linear regression strategy, shortening the sampling by 2 h and one sampling point without performance loss while simultaneously offering flexibility in sampling times.