Pound foolish and penny wise-when will dosing of rifampicin be optimised?

Therapeutic drug monitoring in tuberculosis

PURPOSE

Therapeutic drug monitoring (TDM) is a standard clinical procedure that uses the pharmacokinetic and pharmacodynamic parameters of the drug in the body to determine the optimal dose. The pharmacokinetic variability of the drug(s) is a significant contributor to poor treatment outcomes, including the development of acquired drug resistance. TDM aids in dose optimization and improves outcomes while lessening drug toxicity. TDM is used to manage patients with tuberculosis (TB) who exhibit a slow response to therapy, despite good compliance and drug-susceptible organisms. Additional indications include patients at risk of malabsorption or delayed absorption of TB drugs and patients with drug-drug interaction and drug toxicity, which confirm compliance with therapy. TDM usually requires two blood samples: the 2 h and the 6 h post-dose. This narrative review will discuss the pharmacokinetics and pharmacodynamics of TB drugs, determinants of poor response to therapy, indications of TDM, methods of performing TDM, and its interpretations.

METHODS

This is a narrative review. We searched PubMed, Embase, and the CINAHL from inception to April 2024. We used the following search terms: tuberculosis, therapeutic drug monitoring, anti-TB drugs, pharmacokinetics, pharmacodynamics, limited sample strategies, diabetes and TB, HIV and TB, and multidrug-resistant TB. All types of articles were selected.

RESULTS

TDM is beneficial in managing TB, especially in patients with slow responses, drug-resistance TB, recurrent TB, and comorbidities such as diabetes mellitus and human immunodeficiency virus infection.

CONCLUSION

TDM is beneficial for improving outcomes, reducing the risk of acquired drug resistance, and avoiding side effects.

The quest to deliver high-dose rifampicin: can the inhaled approach help?

INTRODUCTION

Tuberculosis (TB) is a global health problem that poses a challenge to global treatment programs. Rifampicin is a potent and highly effective drug for TB treatment; however, higher oral doses than the standard dose (10 mg/kg/day) rifampicin may offer better efficacy in TB treatment.

AREAS COVERED

High oral dose rifampicin is not implemented in anti-TB regimens yet and requires about a 3-fold increase in dose for increased efficacy. We discuss inhaled delivery of rifampicin as an alternative or adjunct to oral high-dose rifampicin. Clinical results of safety, tolerability, and patient compliance with antibiotic dry powder inhalers are reviewed.

EXPERT OPINION

Clinical trials suggest that an approximately 3-fold increase in the standard oral dose of rifampicin may be required for better clinical outcomes. On the other hand, animal studies suggest that inhaled rifampicin can deliver a high concentration of the drug to the lungs and achieve approximately double the plasma concentration than that from oral rifampicin. Clinical trials on inhaled antibiotics suggest that dry powder inhalation is a patient-friendly and well-tolerated approach in treating respiratory infections compared to conventional treatments. Rifampicin, a well-known anti-TB drug given orally, is a good candidate for clinical development as a dry powder inhaler.

Dried Blood Spot Sampling to Assess Rifampicin Exposure and Treatment Outcomes among Native and Non-Native Tuberculosis Patients in Paraguay: An Exploratory Study

The aim of this study was to evaluate the difference in drug exposure of rifampicin in native versus non-native Paraguayan populations using dried blood spots (DBS) samples collected utilizing a limited sampling strategy. This was a prospective pharmacokinetic study that enrolled hospitalized tuberculosis (TB) patients from both native and non-native populations receiving oral rifampicin 10 mg/kg once-daily dosing. Steady-state DBS samples were collected at 2, 4, and 6 h after intake of rifampicin. The area under the time concentration curve 0–24 h (AUC0–24) was calculated using a Bayesian population PK model. Rifampicin AUC0–24 < 38.7 mg*h/L was considered as low. The probability of target attainment (PTA) was calculated using AUC0–24/MIC > 271 as a target and estimated MIC values of 0.125 and 0.25 mg/L. In total, 50 patients were included. Native patients (n = 30) showed comparable drug exposure to the non-natives (n = 20), median AUC0–24 24.7 (17.1–29.5 IQR) and 21.6 (15.0–35.4 IQR) mg*h/L (p = 0.66), respectively. Among total patients, only 16% (n = 8) had a rifampicin AUC0–24 > 38.7 mg*h/L. Furthermore, PTA analysis showed that only 12 (24%) of the patients met a target AUC0–24 /MIC ≥ 271, assuming an MIC of 0.125 mg/L, which plummeted to 0% at a wild-type MIC of 0.25 mg/L. We successfully used DBS and limited sampling for the AUC0–24 estimation of rifampicin. Currently, our group, the EUSAT-RCS consortium, is preparing a prospective multinational, multicenter phase IIb clinical trial evaluating the safety and efficacy of high-dose rifampicin (35 mg/kg) in adult subjects using the DBS technique for AUC0–24 estimation.

Optimizing dosing and fixed-dose combinations of rifampicin, isoniazid, and pyrazinamide in pediatric patients with tuberculosis: a prospective population pharmacokinetic study

BACKGROUND

In 2010, the WHO revised dosing guidelines for treatment of childhood tuberculosis. Our aim was to investigate first-line antituberculosis drug exposures under these guidelines, explore dose optimization using the current dispersible fixed-dose combination (FDC) table of rifampicin/isoniazid/pyrazinamide; 75/50/150 mg , and suggest a new FDC with revised weight-bands.

METHODS

Children with drug-susceptible tuberculosis in Malawi and South Africa underwent pharmacokinetic sampling while receiving first-line tuberculosis drugs as single formulations according the 2010 WHO recommended doses. Nonlinear mixed-effects modelling and simulation was used to design the optimal FDC and weight-band dosing strategy for achieving the pharmacokinetic targets based on literature-derived adult AUC0-24h for rifampicin (38.7-72.9) isoniazid (11.6-26.3) and pyrazinamide (233-429 mg∙h/L).

RESULTS

180 children (42% female; 13.9% HIV-infected; median [range] age 1.9 [0.22-12] years; weight 10.7 [3.20-28.8] kg) were administered 1, 2, 3, or 4 FDC tablets (rifampicin/isoniazid/pyrazinamide 75/50/150 mg) daily for 4-8, 8-12, 12-16, and 16-25 kg weight-bands, respectively. Rifampicin exposure (for weight and age) was up to 50% lower than in adults. Increasing the tablet number resulted in adequate rifampicin but relatively high isoniazid and pyrazinamide exposures. Administering 1, 2, 3, or 4 optimized FDC tablets (rifampicin/isoniazid/pyrazinamide 120/35/130 mg) to children <6, 6-13, 13-20 and 20-25 kg, and 0.5 tablet in <3-month-olds with immature metabolism, improved exposures to all three drugs.

CONCLUSION

Current pediatric FDC doses resulted in low rifampicin exposures. Optimal dosing of all drugs cannot be achieved with the current FDCs. We propose a new FDC formulation and revised weight-bands.

Recurrent Tuberculosis Disease in Singapore

Background

Previously treated (ie, recurrent) tuberculosis (TB) cases account for approximately 7%-8% of incident TB globally and in Singapore. Molecular fingerprinting has enabled the differentiation of these patients into relapsed or reinfection cases.

Methods

Patient demographics, disease characteristics, and treatment information were obtained from the national TB notification registry and TB Control Unit. We performed a retrospective, case-control study to evaluate factors associated with recurrent TB disease in Singapore citizens and permanent residents with culture-positive TB from 2006 to 2013 and who developed a second episode of culture-positive TB up to 2016 using multivariable logistic regression analyses.

Results

Ninety-one cases with culture-positive first and recurrent TB disease episodes were identified. Recurrent TB was associated with age ≥60 years (adjusted odds ratio [aOR], 1.98 [95% confidence interval {CI}, 1.09-3.61), male sex (aOR, 2.29 [95% CI, 1.22-4.51]), having concomitant pulmonary and extrapulmonary TB (aOR, 3.10 [95% CI, 1.59-6.10]) and extrapulmonary TB alone (aOR, 3.82 [95% CI, 1.12-13.31]), and was less likely in non-Malays (aOR, 0.52 [95% CI, .27-.99]). DNA fingerprinting results for both episodes in 49 cases differentiated these into 28 relapsed and 21 reinfection cases. Relapse was associated with having concomitant pulmonary and extrapulmonary TB (aOR, 9.24 [95% CI, 2.50-42.42]) and positive sputum acid-fast bacilli smear (aOR, 3.95 [95% CI, 1.36-13.10]).

Conclusions

Relapse and reinfection contributed to 57% and 43%, respectively, of recurrent TB in Singapore. Our study highlights the underappreciated association of concomitant pulmonary and extrapulmonary TB as a significant risk factor for disease relapse.

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.

Evolution of rifampicin treatment for tuberculosis

Rifampicin was discovered in 1965 and remains one of the most important drugs in tuberculosis treatment that is valued for its sterilizing activity and ability to shorten treatment. Antimicrobial activity of rifampicin was initially proved in vitro; subsequently numerous in vivo studies showed the bactericidal properties and dose-dependent effect of rifampicin. Rifampicin was first during the late 1960s to treat patients suffering from chronic drug-resistant pulmonary TB. Decades later, rifampicin continues to be studied with particular emphasis on whether higher doses could shorten the duration of treatment without increasing relapse or having adverse effects. Lesion-specific drug penetration and pharmacokinetics of rifampicin are improving our understanding of effective concentration while potentially refining drug regimen designs. Another prospective aspect of high-dose rifampicin is its potential use in treating discrepant mutation thereby eliminating the need for MDR treatment. To date, several clinical trials have shown the safety, efficacy, and tolerability of high-dose rifampicin. Currently, high-dose rifampicin has been used successfully in a routine clinical setting for the treatment of high-risk patients. However, the WHO and other relevant policy makers have not committed to implementing a controlled rollout thereof. This review describes the course that rifampicin has travelled to the present-day exploration of high-dose rifampicin treatment.

High-dose rifampicin in tuberculosis: Experiences from a Dutch tuberculosis centre

BACKGROUND

Recent evidence suggests that higher rifampicin doses may improve tuberculosis (TB) treatment outcome.

METHODS

In this observational cohort study we evaluated all TB patients who were treated with high-dose rifampicin (> 10 mg/kg daily) in our reference centre, from January 2008 to May 2018. Indications, achieved plasma rifampicin exposures, safety and tolerability were evaluated.

RESULTS

Eighty-eight patients were included. The main indications were low plasma concentrations (64.7%) and severe illness (29.5%), including central nervous system TB. Adjusted rifampicin dosages ranged from 900 mg to a maximum of 2400 mg (corresponding to 32 mg/kg) per day. Patients with severe illness received high-dose rifampicin immediately, the others had a higher dosage guided by therapeutic drug monitoring. Four patients developed hepatotoxicity, of which two were proven due to isoniazid. Re-introduction of high-dose rifampicin was successful in all four. Eighty-seven patients tolerated high-dose rifampicin well throughout treatment. Only one patient required a dose reduction due to gastro-intestinal disturbance.

CONCLUSION

High-dose rifampicin, used in specific groups of patients in our clinical setting, is safe and well-tolerated for the whole treatment duration. Measurement of drug exposures could be used as a tool/guide to increase rifampicin dosage if a reduced medication absorption or a poor treatment outcome is suspected. We suggest to administer high-dose rifampicin to patients with severe manifestations of TB or low rifampicin exposure to improve treatment outcome.

Evaluation of Carbapenems for Treatment of Multi- and Extensively Drug-Resistant Mycobacterium tuberculosis

Multi- and extensively drug-resistant tuberculosis (M/XDR-TB) has become an increasing threat not only in countries where the TB burden is high but also in affluent regions, due to increased international travel and globalization. Carbapenems are earmarked as potentially active drugs for the treatment of Mycobacterium tuberculosis To better understand the potential of carbapenems for the treatment of M/XDR-TB, the aim of this review was to evaluate the literature on currently available in vitro, in vivo, and clinical data on carbapenems in the treatment of M. tuberculosis and to detect knowledge gaps, in order to target future research. In February 2018, a systematic literature search of PubMed and Web of Science was performed. Overall, the results of the studies identified in this review, which used a variety of carbapenem susceptibility tests on clinical and laboratory strains of M. tuberculosis, are consistent. In vitro, the activity of carbapenems against M. tuberculosis is increased when used in combination with clavulanate, a BLaC inhibitor. However, clavulanate is not commercially available alone, and therefore, it is impossible in practice to prescribe carbapenems in combination with clavulanate at this time. Few in vivo studies have been performed, including one prospective, two observational, and seven retrospective clinical studies to assess the effectiveness, safety, and tolerability of three different carbapenems (imipenem, meropenem, and ertapenem). We found no clear evidence at the present time to select one particular carbapenem among the different candidate compounds to design an effective M/XDR-TB regimen. Therefore, more clinical evidence and dose optimization substantiated by hollow-fiber infection studies are needed to support repurposing carbapenems for the treatment of M/XDR-TB.

Optimization of dosing regimens of isoniazid and rifampicin in children with tuberculosis in India

AIMS

Pharmacokinetic studies in the past have shown inadequate antituberculosis drug levels in children with the currently available dosing regimens. This study attempted to investigate the pharmacokinetics of isoniazid and rifampicin, when used in children, and to optimize their dosing regimens.

METHODS

Data were collected from 41 children, aged 2-16 years, who were being treated with antituberculosis drugs for at least 2 months. Concentration measurements were done for 6 h and analysed using a nonlinear, mixed-effects model.

RESULTS

Isoniazid pharmacokinetics were described by a one-compartment disposition model with a transit absorption model (fixed, n = 5). A mixture model was used to identify the slow and fast acetylator subgroups. Rifampicin was described by a one-compartment disposition model with a transit absorption model (fixed, n = 9). Body weight was added to the clearance and volume of distribution of both the drugs using an allometric function. Simulations with the isoniazid model showed that 84.9% of the population achieved therapeutic peak serum concentration with the planned fixed-dose combination regimen. Simulations with the rifampicin model showed that only about 28.8% of the simulated population achieve the therapeutic peak serum concentration with the fixed-dose combination regimen. A novel regimen for rifampicin, with an average dose of 35 mg kg^-1 , was found to provide adequate drug exposure in most children.

CONCLUSIONS

The exposure to isoniazid is adequate with present regimens. For rifampicin, a novel dosing regimen was developed to ensure adequate drug concentrations in children. However, further studies are required to assess the dose-effect relationship of higher doses of rifampicin.