Pharmacokinetics and safety of first-line tuberculosis drugs rifampin, isoniazid, ethambutol, and pyrazinamide during pregnancy and postpartum: results from IMPAACT P1026s

Physiological changes during pregnancy may alter the pharmacokinetics (PK) of antituberculosis drugs. The International Maternal Pediatric Adolescent AIDS Clinical Trials Network P1026s was a multicenter, phase IV, observational, prospective PK and safety study of antiretroviral and antituberculosis drugs administered as part of clinical care in pregnant persons living with and without HIV. We assessed the effects of pregnancy on rifampin, isoniazid, ethambutol, and pyrazinamide PK in pregnant and postpartum (PP) persons without HIV treated for drug-susceptible tuberculosis disease. Daily antituberculosis treatment was prescribed following World Health Organization-recommended weight-band dosing guidelines. Steady-state 12-hour PK profiles of rifampin, isoniazid, ethambutol, and pyrazinamide were performed during second trimester (2T), third trimester (3T), and 2-8 of weeks PP. PK parameters were characterized using noncompartmental analysis, and comparisons were made using geometric mean ratios (GMRs) with 90% confidence intervals (CI). Twenty-seven participants were included: 11 African, 9 Asian, 3 Hispanic, and 4 mixed descent. PK data were available for 17, 21, and 14 participants in 2T, 3T, and PP, respectively. Rifampin and pyrazinamide AUC0-24 and C max in pregnancy were comparable to PP with the GMR between 0.80 and 1.25. Compared to PP, isoniazid AUC0-24 was 25% lower and C max was 23% lower in 3T. Ethambutol AUC0-24 was 39% lower in 3T but limited by a low PP sample size. In summary, isoniazid and ethambutol concentrations were lower during pregnancy compared to PP concentrations, while rifampin and pyrazinamide concentrations were similar. However, the median AUC0-24 for rifampin, isoniazid, and pyrazinamide met the therapeutic targets. The clinical impact of lower isoniazid and ethambutol exposure during pregnancy needs to be determined.

Evaluating pediatric tuberculosis dosing guidelines: A model-based individual data pooled analysis

BACKGROUND

The current World Health Organization (WHO) pediatric tuberculosis dosing guidelines lead to suboptimal drug exposures. Identifying factors altering the exposure of these drugs in children is essential for dose optimization. Pediatric pharmacokinetic studies are usually small, leading to high variability and uncertainty in pharmacokinetic results between studies. We pooled data from large pharmacokinetic studies to identify key covariates influencing drug exposure to optimize tuberculosis dosing in children.

METHODS AND FINDINGS

We used nonlinear mixed-effects modeling to characterize the pharmacokinetics of rifampicin, isoniazid, and pyrazinamide, and investigated the association of human immunodeficiency virus (HIV), antiretroviral therapy (ART), drug formulation, age, and body size with their pharmacokinetics. Data from 387 children from South Africa, Zambia, Malawi, and India were available for analysis; 47% were female and 39% living with HIV (95% on ART). Median (range) age was 2.2 (0.2 to 15.0) years and weight 10.9 (3.2 to 59.3) kg. Body size (allometry) was used to scale clearance and volume of distribution of all 3 drugs. Age affected the bioavailability of rifampicin and isoniazid; at birth, children had 48.9% (95% confidence interval (CI) [36.0%, 61.8%]; p < 0.001) and 64.5% (95% CI [52.1%, 78.9%]; p < 0.001) of adult rifampicin and isoniazid bioavailability, respectively, and reached full adult bioavailability after 2 years of age for both drugs. Age also affected the clearance of all drugs (maturation), children reached 50% adult drug clearing capacity at around 3 months after birth and neared full maturation around 3 years of age. While HIV per se did not affect the pharmacokinetics of first-line tuberculosis drugs, rifampicin clearance was 22% lower (95% CI [13%, 28%]; p < 0.001) and pyrazinamide clearance was 49% higher (95% CI [39%, 57%]; p < 0.001) in children on lopinavir/ritonavir; isoniazid bioavailability was reduced by 39% (95% CI [32%, 45%]; p < 0.001) when simultaneously coadministered with lopinavir/ritonavir and was 37% lower (95% CI [22%, 52%]; p < 0.001) in children on efavirenz. Simulations of 2010 WHO-recommended pediatric tuberculosis doses revealed that, compared to adult values, rifampicin exposures are lower in most children, except those younger than 3 months, who experience relatively higher exposure for all drugs, due to immature clearance. Increasing the rifampicin doses in children older than 3 months by 75 mg for children weighing <25 kg and 150 mg for children weighing >25 kg could improve rifampicin exposures. Our analysis was limited by the differences in availability of covariates among the pooled studies.

CONCLUSIONS

Children older than 3 months have lower rifampicin exposures than adults and increasing their dose by 75 or 150 mg could improve therapy. Altered exposures in children with HIV is most likely caused by concomitant ART and not HIV per se. The importance of the drug-drug interactions with lopinavir/ritonavir and efavirenz should be evaluated further and considered in future dosing guidance.

TRIAL REGISTRATION

ClinicalTrials.gov registration numbers; NCT02348177, NCT01637558, ISRCTN63579542.

Is there a need to optimise pyrazinamide doses in patients with tuberculosis? A systematic review

Pyrazinamide (PZA) is a first-line antituberculosis drug with potent sterilising activity. Variability in drug exposure may translate into suboptimal treatment responses. This systematic review, conducted according to PRISMA guidelines, aimed to evaluate the concentration-effect relationship. In vitro/in vivo studies had to contain information on the infection model, PZA dose and concentration, and microbiological outcome. Human studies had to present information on PZA dose, measures of drug exposure and maximum concentration, and microbiological response parameter or overall treatment outcome. A total of 34 studies were assessed, including in vitro (n = 2), in vivo (n = 3) and clinical studies (n = 29). Intracellular and extracellular models demonstrated a direct correlation between PZA dose of 15-50 mg/kg/day and reduction in bacterial count between 0.50-27.7 log10 CFU/mL. Consistent with this, higher PZA doses (>150 mg/kg) were associated with a greater reduction in bacterial burden in BALB/c mice models. Human pharmacokinetic studies displayed a linear positive correlation between PZA dose (i.e. 21.4-35.7 mg/kg/day) and drug exposure (AUC range 220.6-514.5 mg·h/L). Additionally, human studies confirmed a dose-effect relationship, with an increased 2-month sputum culture conversion rate at AUC/MIC targets of 8.4-11.3 with higher exposure/susceptibility ratios leading to greater efficacy. A 5-fold variability in AUC was observed at PZA dose of 25 mg/kg. A direct concentration-effect relationship and increased treatment efficacy with higher PZA exposure to susceptibility ratios was observed. Taking into account variability in drug exposure and treatment response, further studies on dose optimisation are justified.

Sex Differences in TB Clinical Presentation, Drug Exposure, and Treatment Outcomes in India

BACKGROUND

The role of sex differences in clinical presentation, TB drug pharmacokinetic variables, and treatment outcomes is unclear.

RESEARCH QUESTION

What is the effect of sex on TB disease severity, drug exposure, and treatment outcome?

STUDY DESIGN AND METHODS

This study was a prospective cohort study conducted in India. It assessed TB disease severity; risk of unfavorable treatment outcomes (failure, recurrence, and death) according to sex; and risk factors for unfavorable outcomes stratified according to sex. Effects of sex on the pharmacokinetic variables (maximum concentration and area under the curve) of rifampicin, isoniazid, and pyrazinamide were estimated by using noncompartmental analyses.

RESULTS

Of 1,541 people with microbiologically confirmed TB, 567 (37%) were women. Women had a lower risk of high mycobacterial burden (smear grade ≥ 2 and/or time to detection < 7 days) with an adjusted OR of 0.70 (95% CI, 0.56-0.87). Among the 744 participants who were followed up prospectively, 261 (35%) were women. Women had a lower risk of unfavorable treatment outcomes (adjusted incidence risk ratio, 0.60; 95% CI, 0.43-0.85), mostly because recurrence was lower (adjusted incidence risk ratio, 0.45; 95% CI, 0.23-0.86). Isoniazid (but not rifampicin and pyrazinamide) maximum concentration and area under the curve were significantly higher among women (P < .01) than men. Among women, unfavorable outcomes were more likely among those with cavitary disease, but among men, increased risk of unfavorable outcomes was associated with alcohol use, higher BMI, and lower glycated hemoglobin level.

INTERPRETATION

Women present with lower mycobacterial burden, achieve higher TB drug exposure, and are less likely to have unfavorable treatment outcomes than men. Strategies to improve TB treatment success should take into account sex differences in risk factors for unfavorable outcomes.

Drug concentration at the site of disease in children with pulmonary tuberculosis

BACKGROUND

Current TB treatment for children is not optimized to provide adequate drug levels in TB lesions. Dose optimization of first-line antituberculosis drugs to increase exposure at the site of disease could facilitate more optimal treatment and future treatment-shortening strategies across the disease spectrum in children with pulmonary TB.

OBJECTIVES

To determine the concentrations of first-line antituberculosis drugs at the site of disease in children with intrathoracic TB.

METHODS

We quantified drug concentrations in tissue samples from 13 children, median age 8.6 months, with complicated forms of pulmonary TB requiring bronchoscopy or transthoracic surgical lymph node decompression in a tertiary hospital in Cape Town, South Africa. Pharmacokinetic models were used to describe drug penetration characteristics and to simulate concentration profiles for bronchoalveolar lavage, homogenized lymph nodes, and cellular and necrotic lymph node lesions.

RESULTS

Isoniazid, rifampicin and pyrazinamide showed lower penetration in most lymph node areas compared with plasma, while ethambutol accumulated in tissue. None of the drugs studied was able to reach target concentration in necrotic lesions.

CONCLUSIONS

Despite similar penetration characteristics compared with adults, low plasma exposures in children led to low site of disease exposures for all drugs except for isoniazid.

Population Pharmacokinetic Modelling of Pyrazinamide and Pyrazinoic Acid in Patients with Multi-Drug Resistant Tuberculosis

BACKGROUND AND OBJECTIVES

Pyrazinamide, a drug used in the regimen for the treatment of drug-sensitive tuberculosis, is also used for the treatment of multidrug-resistant tuberculosis (MDR-TB). We aimed to describe the population pharmacokinetics of pyrazinamide and its major metabolite, pyrazinoic acid, in patients with MDR-TB and characterise the effects of demographic variables.

METHODS

This was a non-randomised clinical study involving 51 adult patients admitted for the intensive phase of MDR-TB treatment. Blood samples were collected at pre-dose and at 0.5, 1, 1.5, 2, 3, 4, 8, 16 and 24 h after drug administration. Plasma concentrations of pyrazinamide and pyrazinoic acid were analysed using a validated LC-MS/MS method. Nonlinear mixed-effects modelling using Monolix 2018R1 software was employed to estimate population pharmacokinetic parameters.

RESULTS

A one-compartment pharmacokinetic model with transit compartment absorption process and first-order elimination best described the pyrazinamide and pyrazinoic acid concentration-time data. The estimated population pharmacokinetic parameters were 0.7 h, 3.38 h^-1, 57.1 l, 4.37 L/h and 10.5 L/h for mean transit time, absorption rate constant, apparent distribution volume for pyrazinamide, and apparent clearance for pyrazinamide and pyrazinoic acid (CLm/F), respectively. These parameters were not affected by patient age, HIV status or sex. The parameter variability in CLm/F was the highest (83.5%), while the rest of the parameters ranged from 16.2 to 58%.

CONCLUSIONS

The developed population pharmacokinetic model adequately described the disposition of pyrazinamide and pyrazinoic acid and can be useful for dose determination of pyrazinamide in patients with MDR-TB.

Pharmacological and Molecular Mechanisms Behind the Sterilizing Activity of Pyrazinamide

Inclusion of pyrazinamide (PZA) in the tuberculosis (TB) drug regimen during the 1970s enabled a reduction in treatment duration from 12 to 6 months. PZA has this remarkable effect in patients despite displaying poor potency against Mycobacterium tuberculosis (Mtb) in vitro. The pharmacological basis for the in vivo sterilizing activity of the drug has remained obscure and its bacterial target controversial. Recently it was shown that PZA penetrates necrotic caseous TB lung lesions and kills nongrowing, drug-tolerant bacilli. Furthermore, it was uncovered that PZA inhibits bacterial Coenzyme A biosynthesis. It may block this pathway by triggering degradation of its target, aspartate decarboxylase. The elucidation of the pharmacological and molecular mechanisms of PZA provides the basis for the rational discovery of the next-generation PZA with improved in vitro potency while maintaining attractive pharmacological properties.

Tuberculosis drugs' distribution and emergence of resistance in patient's lung lesions: A mechanistic model and tool for regimen and dose optimization

BACKGROUND

The sites of mycobacterial infection in the lungs of tuberculosis (TB) patients have complex structures and poor vascularization, which obstructs drug distribution to these hard-to-reach and hard-to-treat disease sites, further leading to suboptimal drug concentrations, resulting in compromised TB treatment response and resistance development. Quantifying lesion-specific drug uptake and pharmacokinetics (PKs) in TB patients is necessary to optimize treatment regimens at all infection sites, to identify patients at risk, to improve existing regimens, and to advance development of novel regimens. Using drug-level data in plasma and from 9 distinct pulmonary lesion types (vascular, avascular, and mixed) obtained from 15 hard-to-treat TB patients who failed TB treatments and therefore underwent lung resection surgery, we quantified the distribution and the penetration of 7 major TB drugs at these sites, and we provide novel tools for treatment optimization.

METHODS AND FINDINGS

A total of 329 plasma- and 1,362 tissue-specific drug concentrations from 9 distinct lung lesion types were obtained according to optimal PK sampling schema from 15 patients (10 men, 5 women, aged 23 to 58) undergoing lung resection surgery (clinical study NCT00816426 performed in South Korea between 9 June 2010 and 24 June 2014). Seven major TB drugs (rifampin [RIF], isoniazid [INH], linezolid [LZD], moxifloxacin [MFX], clofazimine [CFZ], pyrazinamide [PZA], and kanamycin [KAN]) were quantified. We developed and evaluated a site-of-action mechanistic PK model using nonlinear mixed effects methodology. We quantified population- and patient-specific lesion/plasma ratios (RPLs), dynamics, and variability of drug uptake into each lesion for each drug. CFZ and MFX had higher drug exposures in lesions compared to plasma (median RPL 2.37, range across lesions 1.26-22.03); RIF, PZA, and LZD showed moderate yet suboptimal lesion penetration (median RPL 0.61, range 0.21-2.4), while INH and KAN showed poor tissue penetration (median RPL 0.4, range 0.03-0.73). Stochastic PK/pharmacodynamic (PD) simulations were carried out to evaluate current regimen combinations and dosing guidelines in distinct patient strata. Patients receiving standard doses of RIF and INH, who are of the lower range of exposure distribution, spent substantial periods (>12 h/d) below effective concentrations in hard-to-treat lesions, such as caseous lesions and cavities. Standard doses of INH (300 mg) and KAN (1,000 mg) did not reach therapeutic thresholds in most lesions for a majority of the population. Drugs and doses that did reach target exposure in most subjects include 400 mg MFX and 100 mg CFZ. Patients with cavitary lesions, irrespective of drug choice, have an increased likelihood of subtherapeutic concentrations, leading to a higher risk of resistance acquisition while on treatment. A limitation of this study was the small sample size of 15 patients, performed in a unique study population of TB patients who failed treatment and underwent lung resection surgery. These results still need further exploration and validation in larger and more diverse cohorts.

CONCLUSIONS

Our results suggest that the ability to reach and maintain therapeutic concentrations is both lesion and drug specific, indicating that stratifying patients based on disease extent, lesion types, and individual drug-susceptibility profiles may eventually be useful for guiding the selection of patient-tailored drug regimens and may lead to improved TB treatment outcomes. We provide a web-based tool to further explore this model and results at http://saviclab.org/tb-lesion/.

Efficacy of pyrazinoic acid dry powder aerosols in resolving necrotic and non-necrotic granulomas in a guinea pig model of tuberculosis

New therapeutic strategies are needed to treat drug resistant tuberculosis (TB) and to improve treatment for drug sensitive TB. Pyrazinamide (PZA) is a critical component of current first-line TB therapy. However, the rise in PZA-resistant TB cases jeopardizes the future utility of PZA. To address this problem, we used the guinea pig model of TB and tested the efficacy of an inhaled dry powder combination, referred to as Pyrazinoic acid/ester Dry Powder (PDP), which is comprised of pyrazinoic acid (POA), the active moiety of PZA, and pyrazinoic acid ester (PAE), which is a PZA analog. Both POA and PAE have the advantage of being able to act on PZA-resistant Mycobacterium tuberculosis. When used in combination with oral rifampicin (R), inhaled PDP had striking effects on tissue pathology. Effects were observed in lungs, the site of delivery, but also in the spleen and liver indicating both local and systemic effects of inhaled PDP. Tissue granulomas that harbor M. tuberculosis in a persistent state are a hallmark of TB and they pose a challenge for therapy. Compared to other treatments, which preferentially cleared non-necrotic granulomas, R+PDP reduced necrotic granulomas more effectively. The increased ability of R+PDP to act on more recalcitrant necrotic granulomas suggests a novel mechanism of action. The results presented in this report reveal the potential for developing therapies involving POA that are optimized to target necrotic as well as non-necrotic granulomas as a means of achieving more complete sterilization of M. tuberculosis bacilli and preventing disease relapse when therapy ends.

Plasma levels of Rifampicin and Pyrazinamide with pre and post meal administration in tuberculosis patients

CONTEXT

Various factors affect plasma concentrations of antitubercular drugs in different populations so dosing schedule should be adjusted after therapeutic drug monitoring.

AIMS

To study variability in plasma concentrations of Rifampicin and Pyrazinamide with pre and post-meal administration of drugs in tuberculosis patients.

METHODS AND MATERIAL

52 patients of pulmonary tuberculosis, divided in to two groups, pre and post-meal through systemic randomization. After taking pre-dose sample, drugs were administered according to the group. Samples were withdrawn at 2, 4, 6, and 10h after drug administration. Analysis of samples was done using HPLC.

RESULTS

Mean±1SD of C_max of Rifampicin was 7.75±2.82μg/ml, mean±1SD of AUC_0-10 was 42.17±17.25μgh/ml, adjusted T_max was 4.25h. In pre-meal samples, the corresponding values were 7.75±2.88μg/ml, 42.83±18.47μgh/ml, 3.76h and in post-meal samples 8.03±2.30μg/ml, 41.56±16.46μgh/ml and 4.75h. Mean±1SD of C_max levels of Pyrazinamide was 54.49±21.86μg/ml, mean±1SD of AUC_0-10 was 337.94±124.28μgh/ml and adjusted T_max was 3.49h. In pre-meal samples the corresponding values were 52.00±19.13μg/ml, 329.96±112.11μgh/ml, 3.23h, and in post-meal samples 57.43±23.61μg/ml, 345.58±136.99μgh/ml, 3.54h.

CONCLUSION

There is huge variability in the plasma levels of Rifampicin and Pyrazinamide in population of this sub-himalayan region.

Cohort profile of a study on outcomes related to tuberculosis and antiretroviral drug concentrations in Uganda: design, methods and patient characteristics of the SOUTH study

PURPOSE

Tuberculosis (TB) is a leading cause of death among people living with HIV in sub-Saharan Africa. Several factors influence the efficacy of TB treatment by leading to suboptimal drug concentrations and subsequently affecting treatment outcome. The aim of this cohort is to determine the association between anti-TB drug concentrations and TB treatment outcomes.

PARTICIPANTS

Patients diagnosed with new pulmonary TB at the integrated TB-HIV outpatient clinic in Kampala, Uganda, were enrolled into the study and started on first-line anti-TB treatment.

FINDINGS TO DATE

Between April 2013 and April 2015, the cohort enrolled 268 patients coinfected with TB/HIV ; 57.8% are male with a median age of 34 years (IQR 29-40). The median time between the diagnosis of HIV and the diagnosis of TB is 2 months (IQR 0-22.5). The majority of the patients are antiretroviral therapy naive (75.4%). Our population is severely immunosuppressed with a median CD4 cell count at enrolment of 163 cells/µL (IQR 46-298). Ninety-nine per cent of the patients had a diagnosis of pulmonary TB confirmed by sputum microscopy, Xpert/RIF or culture and 203 (75.7%) have completed TB treatment with 5099 aliquots of blood collected for pharmacokinetic analysis.

FUTURE PLANS

This cohort provides a large database of well-characterised patients coinfected with TB/HIV which will facilitate the description of the association between serum drug concentrations and TB treatment outcomes as well as provide a research platform for future substudies including evaluation of virological outcomes.

TRIAL REGISTRATION NUMBER

NCT01782950; Pre-results.

Concentration-Dependent Antagonism and Culture Conversion in Pulmonary Tuberculosis

BACKGROUND

There is scant evidence to support target drug exposures for optimal tuberculosis outcomes. We therefore assessed whether pharmacokinetic/pharmacodynamic (PK/PD) parameters could predict 2-month culture conversion.

METHODS

One hundred patients with pulmonary tuberculosis (65% human immunodeficiency virus coinfected) were intensively sampled to determine rifampicin, isoniazid, and pyrazinamide plasma concentrations after 7-8 weeks of therapy, and PK parameters determined using nonlinear mixed-effects models. Detailed clinical data and sputum for culture were collected at baseline, 2 months, and 5-6 months. Minimum inhibitory concentrations (MICs) were determined on baseline isolates. Multivariate logistic regression and the assumption-free multivariate adaptive regression splines (MARS) were used to identify clinical and PK/PD predictors of 2-month culture conversion. Potential PK/PD predictors included 0- to 24-hour area under the curve (AUC0-24), maximum concentration (Cmax), AUC0-24/MIC, Cmax/MIC, and percentage of time that concentrations persisted above the MIC (%TMIC).

RESULTS

Twenty-six percent of patients had Cmax of rifampicin <8 mg/L, pyrazinamide <35 mg/L, and isoniazid <3 mg/L. No relationship was found between PK exposures and 2-month culture conversion using multivariate logistic regression after adjusting for MIC. However, MARS identified negative interactions between isoniazid Cmax and rifampicin Cmax/MIC ratio on 2-month culture conversion. If isoniazid Cmax was <4.6 mg/L and rifampicin Cmax/MIC <28, the isoniazid concentration had an antagonistic effect on culture conversion. For patients with isoniazid Cmax >4.6 mg/L, higher isoniazid exposures were associated with improved rates of culture conversion.

CONCLUSIONS

PK/PD analyses using MARS identified isoniazid Cmax and rifampicin Cmax/MIC thresholds below which there is concentration-dependent antagonism that reduces 2-month sputum culture conversion.

The biodistribution of 5-[18F]fluoropyrazinamide in Mycobacterium tuberculosis-infected mice determined by positron emission tomography

5-[¹⁸F]F-pyrazinamide (5-[¹⁸F]F-PZA), a radiotracer analog of the first-line tuberculosis drug pyrazinamide (PZA), was employed to determine the biodistribution of PZA using PET imaging and ex vivo analysis. 5-[¹⁸F]F-PZA was synthesized in 60 min using a halide exchange reaction. The overall decay-corrected yield of the reaction was 25% and average specific activity was 2.6 × 10⁶ kBq (70 mCi)/μmol. The biodistribution of 5-[¹⁸F]F-PZA was examined in a pulmonary Mycobacterium tuberculosis mouse model, where rapid distribution of the tracer to the lung, heart, liver, kidney, muscle, and brain was observed. The concentration of 5-[¹⁸F]F-PZA was not significantly different between infected and uninfected lung tissue. Biochemical and microbiological studies revealed substantial differences between 5-F-PZA and PZA. 5-F-PZA was not a substrate for pyrazinamidase, the bacterial enzyme that activates PZA, and the minimum inhibitory concentration for 5-F-PZA against M. tuberculosis was more than 100-fold higher than that for PZA.

Pharmacokinetics of the First-Line Antituberculosis Drugs in Ghanaian Children with Tuberculosis with or without HIV Coinfection

Although human immunodeficiency virus (HIV) coinfection is the most important risk factor for a poor antituberculosis (anti-TB) treatment response, its effect on the pharmacokinetics of the first-line drugs in children is understudied. This study examined the pharmacokinetics of the four first-line anti-TB drugs in children with TB with and without HIV coinfection. Ghanaian children with TB on isoniazid, rifampin, pyrazinamide, and ethambutol for at least 4 weeks had blood samples collected predose and at 1, 2, 4, and 8 hours postdose. Drug concentrations were determined by validated liquid chromatography-mass spectrometry methods and pharmacokinetic parameters calculated using noncompartmental analysis. The area under the concentration-time curve from 0 to 8 h (AUC0-8), maximum concentration (Cmax), and apparent oral clearance divided by bioavailability (CL/F) for each drug were compared between children with and without HIV coinfection. Of 113 participants, 59 (52.2%) had HIV coinfection. The baseline characteristics were similar except that the coinfected patients were more likely to have lower weight-for-age and height-for-age Z scores (P < 0.05). Rifampin, pyrazinamide, and ethambutol median body weight-normalized CL/F values were significantly higher, whereas the plasma AUC0-8 values were lower, in the coinfected children than in those with TB alone. In the multivariate analysis, drug dose and HIV coinfection jointly influenced the apparent oral clearance and AUC0-8 for rifampin, pyrazinamide, and ethambutol. Isoniazid pharmacokinetics were not different by HIV coinfection status. HIV coinfection was associated with lower plasma exposure of three of the four first-line anti-TB drugs in children. Whether TB/HIV-coinfected children need higher dosages of rifampin, pyrazinamide, and ethambutol requires further investigation. (This study has been registered at ClinicalTrials.gov under identifier NCT01687504.).

Pharmacokinetics of Rifampin, Isoniazid, Pyrazinamide, and Ethambutol in Infants Dosed According to Revised WHO-Recommended Treatment Guidelines

There are limited pharmacokinetic data for use of the first-line antituberculosis drugs during infancy (<12 months of age), when drug disposition may differ. Intensive pharmacokinetic sampling was performed in infants routinely receiving antituberculosis treatment, including rifampin, isoniazid, pyrazinamide, and ethambutol, using World Health Organization-recommended doses. Regulatory-approved single-drug formulations, including two rifampin suspensions, were used on the sampling day. Assays were conducted using liquid chromatography-mass spectrometry; pharmacokinetic parameters were generated using noncompartmental analysis. Thirty-nine infants were studied; 14 (36%) had culture-confirmed tuberculosis. Fifteen (38%) were premature (<37 weeks gestation); 5 (13%) were HIV infected. The mean corrected age and weight were 6.6 months and 6.45 kg, respectively. The mean maximum plasma concentrations (Cmax) for rifampin, isoniazid, pyrazinamide, and ethambutol were 2.9, 7.9, 41.9, and 1.3 μg/ml, respectively (current recommended adult target concentrations: 8 to 24, 3 to 6, 20 to 50, and 2 to 6 μg/ml, respectively), and the mean areas under the concentration-time curves from 0 to 8 h (AUC0-8) were 12.1, 24.7, 239.4, and 5.1 μg · h/ml, respectively. After adjusting for age and weight, rifampin exposures for the two formulations used differed inCmax(geometric mean ratio [GMR],2.55; 95% confidence interval [CI], 1.47 to 4.41;P= 0.001) and AUC0-8(GMR, 2.52; 95% CI, 1.34 to 4.73;P= 0.005). HIV status was associated with lower pyrazinamideCmax(GMR, 0.85; 95% CI, 0.75 to 0.96;P= 0.013) and AUC0-8(GMR, 0.79; 95% CI, 0.69 to 0.90;P< 0.001) values. No other important differences were observed due to age, weight, prematurity, ethnicity, or gender. In summary, isoniazid and pyrazinamide concentrations in infants compared well with proposed adult target concentrations; ethambutol concentrations were lower but similar to previously reported pediatric studies. The low rifampin exposures require further investigation. (This study has been registered at ClinicalTrials.gov under registration no. NCT01637558.).

Pharmacokinetics of Isoniazid, Pyrazinamide, and Ethambutol in Newly Diagnosed Pulmonary TB Patients in Tanzania

Exposure to lower-than-therapeutic levels of anti-tuberculosis drugs is likely to cause selection of resistant strains of Mycobacterium tuberculosis and treatment failure. The first-line anti-tuberculosis (TB) regimen consists of rifampicin, isoniazid, pyrazinamide, and ethambutol, and correct management reduces risk of TB relapse and development of drug resistance. In this study we aimed to investigate the effect of standard of care plus nutritional supplementation versus standard care on the pharmacokinetics of isoniazid, pyrazinamide and ethambutol among sputum smear positive TB patients with and without HIV. In a clinical trial in 100 Tanzanian TB patients, with or without HIV infection, drug concentrations were determined at 1 week and 2 months post initiation of anti-TB medication. Data was analysed using population pharmacokinetic modelling. The effect of body size was described using allometric scaling, and the effects of nutritional supplementation, HIV, age, sex, CD4+ count, weight-adjusted dose, NAT2 genotype, and time on TB treatment were investigated. The kinetics of all drugs was well characterised using first-order elimination and transit compartment absorption, with isoniazid and ethambutol described by two-compartment disposition models, and pyrazinamide by a one-compartment model. Patients with a slow NAT2 genotype had higher isoniazid exposure and a lower estimate of oral clearance (15.5 L/h) than rapid/intermediate NAT2 genotype (26.1 L/h). Pyrazinamide clearance had an estimated typical value of 3.32 L/h, and it was found to increase with time on treatment, with a 16.3% increase after the first 2 months of anti-TB treatment. The typical clearance of ethambutol was estimated to be 40.7 L/h, and was found to decrease with age, at a rate of 1.41% per year. Neither HIV status nor nutritional supplementations were found to affect the pharmacokinetics of these drugs in our cohort of patients.

Impact of nonlinear interactions of pharmacokinetics and MICs on sputum bacillary kill rates as a marker of sterilizing effect in tuberculosis

The relationships between antituberculosis drug exposure and treatment effects on humans receiving multidrug therapy are complex and nonlinear. In patients on treatment, an analysis of the rate of decline in the sputum bacillary burden reveals two slopes. The first is the α-slope, which is thought to reflect bactericidal effect, followed by a β-slope, which is thought to reflect sterilizing activity. We sought to characterize the effects of standard first-line treatment on sterilizing activity. Fifty-four patients receiving combination therapy for pulmonary tuberculosis in a clinical trial had drug concentrations measured and Mycobacterium tuberculosis isolates available for MIC identification. Sputum sample cultures were performed at baseline and weekly for 8 weeks. A time-to-event model based on the days to positivity in the liquid cultures was used to estimate the β-slope. The pharmacokinetic parameters of rifampin, isoniazid, ethambutol, and pyrazinamide were determined for each patient. Multivariate adaptive regression splines analyses, which simultaneously perform linear and nonlinear analyses, were used to identify the relationships between the predictors and the β-slope. The potential predictors examined included HIV status, lung cavitation, 24-h area under the concentration-time curve (AUC), peak drug concentration (Cmax), AUC/MIC ratio, Cmax/MIC ratio, and the time that that concentration persisted above MIC. A rifampin Cmax of >8.2 mg/liter and a pyrazinamide AUC/MIC of >11.3 were key predictors of the β-slope and interacted positively to increase the β-slope. In patients with a rifampin AUC of <35.4 mg · h/liter, an increase in the pyrazinamide AUC/MIC and/or ethambutol Cmax/MIC increased the β-slope, while increasing isoniazid Cmax decreased it, suggesting isoniazid antagonism. Antibiotic concentrations and MICs interact in a nonlinear fashion as the main drivers of a sterilizing effect. The results suggest that faster speeds of sterilizing effect might be achieved by omitting isoniazid and by increasing rifampin, pyrazinamide, and ethambutol exposures. However, isoniazid and ethambutol exposures may only be of importance when rifampin exposure is low. These findings need confirmation in larger studies. (This study has been registered at controlled-trials.com under registration no. ISRCTN80852505.).

Feasibility of a fixed-dose regimen of pyrazinamide and its impact on systemic drug exposure and liver safety in patients with tuberculosis

Historically, dosing regimens for the treatment of tuberculosis (TB) have been proposed in an empirical manner. Dose selection has often been the result of efficacy trials in which drugs were administered regardless of the magnitude of the effect of demographic factors on drug disposition. This has created challenges for the prescription of fixed-dose combinations with novel therapeutic agents. The objectives of this investigation were to evaluate the impact of body weight on the overall systemic exposure to pyrazinamide (PZA) and to assess whether the use of one fixed dose, without adjustment according to weight, would ensure target exposure and safety requirements across the overall patient population. Using a population pharmacokinetic model, simulation scenarios were explored based on population demographics from clinical trials in TB patients and on historical hepatotoxicity data. The systemic drug exposure (area under the concentration-time curve [AUC]), peak concentrations (the maximum concentration of drug in serum [C(max)]), the time above the MIC (t > MIC), and the risk of hepatotoxicity were evaluated for the current weight-banded regimen and compared to fixed doses under the assumption that pharmacokinetic differences are the primary drivers of toxicity. Evaluation of the standard weight banding reveals that more than 50% of subjects in the weight range of 45 to 55 kg remain below the proposed target exposure to PZA. In contrast, the use of a fixed 1,500-mg dose resulted in a lower proportion of subjects under the target value, with a 0.2% average overall increase in the risk of hepatotoxicity. Our results strongly support the use of a fixed-dose regimen for PZA in coformulation or combination with novel therapeutic agents.

Rapid evaluation in whole blood culture of regimens for XDR-TB containing PNU-100480 (sutezolid), TMC207, PA-824, SQ109, and pyrazinamide

There presently is no rapid method to assess the bactericidal activity of new regimens for tuberculosis. This study examined PNU-100480, TMC207, PA-824, SQ109, and pyrazinamide, singly and in various combinations, against intracellular M. tuberculosis, using whole blood culture (WBA). The addition of 1,25-dihydroxy vitamin D facilitated detection of the activity of TMC207 in the 3-day cultures. Pyrazinamide failed to show significant activity against a PZA-resistant strain (M. bovis BCG), and was not further considered. Low, mid, and high therapeutic concentrations of each remaining drug were tested individually and in a paired checkerboard fashion. Observed bactericidal activity was compared to that predicted by the sum of the effects of individual drugs. Combinations of PNU-100480, TMC207, and SQ109 were fully additive, whereas those including PA-824 were less than additive or antagonistic. The cumulative activities of 2, 3, and 4 drug combinations were predicted based on the observed concentration-activity relationship, published pharmacokinetic data, and, for PNU-100480, published WBA data after oral dosing. The most active regimens, including PNU-100480, TMC207, and SQ109, were predicted to have cumulative activity comparable to standard TB therapy. Further testing of regimens including these compounds is warranted. Measurement of whole blood bactericidal activity can accelerate the development of novel TB regimens.

Blood levels of pyrazinamide in children at doses administered under the Revised National Tuberculosis Control Program

OBJECTIVES

To evaluate the blood levels, pharma-cokinetics and pharmacodynamic indices of pyrazinamide (PZA) in children suffering from tuberculosis, at doses administered under the weight band system of Revised National Tuberculosis Control Program of India (RNTCP) of India.

DESIGN

Prospective, open-label, non-randomized single-dose study.

SETTING

20 children in the age group 5-12 years attending out-patient tuberculosis clinic of a tertiary hospital.

OUTCOME MEASURES

Blood levels of pyrazinamide after single dose administration, as per the weight band system of RNTCP.

RESULTS

Group I (n=7) included children who received pyrazinamide within the recommended 30-35 mg/kg dose (mean 31.9 ± 0.8 mg/kg) and Group II (n=13) included those who received a dose lower than 30 -35 mg/kg (mean 28.1 ± 0.3 mg/kg). The Cmax (95% CI of difference 2.2, 13.2; P=0.008) and AUC (95% CI of difference 28.6, 208.1; P=0.01) were significantly lower in Group II. The duration of time for which the concentration was maintained above 25 ug ml-1 was 4-8 h in Group I and 3-5.5 h in Group II (95% CI of difference 0.1, 2.0; P=0.03). The half life, elimination rate constant, clearance and volume of distribution were comparable in the two groups. The ratios of Cmax and AUC to MIC (25 ug ml-1) in children were lower than that recommended for PZA in adults.

CONCLUSIONS

Lower blood concentrations are being attained in children receiving PZA doses under the existing weight band system of RNTCP of India. The weight bands may need to be revised and dose recommendations be based on pharmacokinetic and efficacy data in children.

Isoniazid, rifampin, ethambutol, and pyrazinamide pharmacokinetics and treatment outcomes among a predominantly HIV-infected cohort of adults with tuberculosis from Botswana

BACKGROUND

We explored the association between antituberculosis drug pharmacokinetics and treatment outcomes among patients with pulmonary tuberculosis in Botswana.

METHODS

Consenting outpatients with tuberculosis had blood samples collected 1, 2, and 6 h after simultaneous isoniazid, rifampin, ethambutol, and pyrazinamide ingestion. Maximum serum concentrations (C(max)) and areas under the serum concentration time curve were determined. Clinical status was monitored throughout treatment.

RESULTS

Of the 225 participants, 36 (16%) experienced poor treatment outcome (treatment failure or death); 155 (69%) were infected with human immunodeficiency virus (HIV). Compared with published standards, low isoniazid C(max) occurred in 84 patients (37%), low rifampin C(max) in 188 (84%), low ethambutol C(max) in 87 (39%), and low pyrazinamide C(max) in 11 (5%). Median rifampin and pyrazinamide levels differed significantly by HIV status and CD4 cell count category. Only pyrazinamide pharmacokinetics were significantly associated with treatment outcome; low pyrazinamide C(max) was associated with a higher risk of documented poor treatment outcome, compared with normal C(max) (50% vs. 16%; P < .01). HIV-infected patients with a CD4 cell count <200 cells/microL had a higher risk of poor treatment outcome (27%) than did HIV-uninfected patients (11%) or HIV-infected patients with a CD4 cell count 200 cells/microL (12%; P = .01). After adjustment for HIV infection and CD4 cell count, patients with low pyrazinamide C(max) were 3 times more likely than patients with normal pyrazinamide C(max) to have poor outcomes (adjusted risk ratio, 3.38; 95% confidence interval, 1.84-6.22).

CONCLUSIONS

Lower than expected antituberculosis drug C(max) occurred frequently, and low pyrazinamide C(max) was associated with poor treatment outcome. Exploring the global prevalence and significance of these findings may suggest modifications in treatment regimens that could improve tuberculosis cure rates.

Pharmacokinetics of pyrazinamide in children with primary progressive disease of lungs

BACKGROUND & OBJECTIVE

As the dosages recommended for children are based on weight, empirical and derived by extrapolation from the studies in adults, pyrazinamide (PZA) pharmacokinetics in children is likely to be different from adults. Limited information exists regarding the pharmacokinetics of PZA in paediatric patients of primary progressive disease (PPD) of lungs. This study aims to look at the changed pharmacokinetics of pyrazinamide in children with PPD of lungs by using reverse phase high-pressure liquid chromatography (HPLC).

METHODS

A total of 40 children (age range 5 to 13 yr) of PPD were receiving pyrazinamide (30 mg/kg/day). On 11(th) day of short course antitubercular therapy, blood samples (two per day from 11(th) to 13(th) day) were collected at 0 h (pre-dose), 1, 2, 3, 4, 8 and 24 h after pyrazinamide administration and concentration of pyrazinamide was estimated by reverse phase high-pressure liquid chromatography. The mean peak serum concentration, the time to reach mean peak serum concentration, total clearance, concentration at time zero, volume of distribution, terminal elimination rate constant, elimination half-life, total area under serum concentration-time curve were measured.

RESULTS

The mean serum concentrations of pyrazinamide were found higher than its minimum inhibitory concentration (20 microg/ml) required to inhibit the growth of tubercle bacilli from 1 to 8 h continuously.

INTERPRETATION & CONCLUSION

Our results suggest that a dose of 30 mg/kg/day achieves much higher concentration of pyrazinamide as compared to its minimum inhibitory concentration (20 microg/ml). Therefore, lowering of pyrazinamide dosage is suggested in children for better patient compliance along with reduction in cost, side-effects and toxicity without compromising its efficacy.

Chemotherapeutic Efficacy of Nanoparticle Encapsulated Antitubercular Drugs

Our objective was to evaluate the chemotherapeutic potential of oral poly lactide-co-glycolide (PLG, a synthetic polymer) nanoparticle encapsulated ethambutol in combination with PLG-nanoparticle encapsulated-(rifampicin + isoniazid + pyrazinamide) in a murine tuberculosis (TB) model. Our formulation was prepared by the multiple emulsion technique and administered orally to mice for the biodistribution, pharmacokinetic, and chemotherapeutic studies. A single oral administration of the formulation to mice could maintain sustained drug levels in the plasma for 5 days and in the organs (lungs, liver, spleen) for 7-9 days. There was a striking improvement in the pharmacokinetic parameters such as half-life and mean residence time as compared with free drugs. The relative/absolute bioavailability of the 4 antituberculosis drugs was enhanced several fold. Repeated administration of the formulation did not produce any hepatotoxicity as assessed on a biochemical basis. In M. tuberculosis H37Rv infected mice, just 3 oral doses of the 4-drug formulation administered at every 10th day resulted in undetectable bacilli in the organs replacing 28 conventional doses of free drugs. We concluded that polymeric nanoparticle based oral 4-drug combination bears significant potential to shorten the duration of TB chemotherapy, besides reducing the dosing frequency.

Pyrazinamide serum levels in childhood tuberculosis

Pyrazinamide (PZA) is one of the first-line drugs in anti-tuberculosis treatment. In the present study, PZA serum levels in 34 children aged 1 to 14 years were measured either after oral application of PZA alone or after combination therapy with isoniazid and rifampicin. Serum levels did not differ statistically with age, in PZA monotherapy or in combination therapy. With a dosage of 30 mg/kg PZA, efficient serum levels were reached. Because PZA is distributed uniformly in the body, serum levels are related to body weight, and a dose of 30 mg/kg bodyweight is appropriate in children.

Effect of Silibinin on the Pharmacokinetics of Pyrazinamide and Pyrazinoic Acid in Rats

Pyrazinamide (PZA) is widely used in combination with other drugs in chemotherapy for tuberculosis. However, the dose-related liver injury is the main adverse effect of PZA and its metabolite [pyrazinoic acid (PA)]. Silibinin is the main flavonoid extracted from milk thistle (Silybum marianum), and it displays hepatoprotective properties. This study investigates the pharmacokinetics of PZA and PA and their interaction with silibinin in rats. The parallel study design was divided into six groups: PZA alone, PZA + long-term silibinin exposure, PZA + concomitant short-term silibinin exposure, PA alone, PA + long-term silibinin exposure, and PA + concomitant short-term silibinin exposure groups. The results indicate that the distribution ratio of PZA from bile to blood [area under the curve (AUC)(bile)/AUC(blood)] in the PZA + long-term silibinin exposure and PZA + concomitant short-term silibinin exposure groups was also not significantly different when compared with the PZA alone group. However, the bile-to-blood distribution ratio of PA was significantly decreased in the PA + long-term silibinin exposure and the PA + concomitant short-term silibinin exposure groups. On PZA administration, the blood, but not bile, levels of PA were markedly increased in the PZA + long-term silibinin exposure and PZA + concomitant short-term silibinin exposure groups, but the bile-to-blood ratio of PA was decreased. These results suggest that the excretion pathway of PA may be blocked by silibinin through xanthine oxidase and hepatobiliary excretion.

Pharmacokinetics and tolerability of a higher rifampin dose versus the standard dose in pulmonary tuberculosis patients

Rifampin is a key drug for tuberculosis (TB) treatment. The available data suggest that the currently applied 10-mg/kg of body weight dose of rifampin may be too low and that increasing the dose may shorten the treatment duration. A double-blind randomized phase II clinical trial was performed to investigate the effect of a higher dose of rifampin in terms of pharmacokinetics and tolerability. Fifty newly diagnosed adult Indonesian TB patients were randomized to receive a standard (450-mg, i.e., 10-mg/kg in Indonesian patients) or higher (600-mg) dose of rifampin in addition to other TB drugs. A full pharmacokinetic curve for rifampin, pyrazinamide, and ethambutol was recorded after 6 weeks of daily TB treatment. Tolerability was assessed during the 6-month treatment period. The geometric means of exposure to rifampin (area under the concentration-time curve from 0 to 24 h [AUC(0-24)]) were increased by 65% (P < 0.001) in the higher-dose group (79.7 mg.h/liter) compared to the standard-dose group (48.5 mg.h/liter). Maximum rifampin concentrations (C(max)) were 15.6 mg/liter versus 10.5 mg/liter (49% increase; P < 0.001). The percentage of patients for whom the rifampin C(max) was > or =8 mg/liter was 96% versus 79% (P = 0.094). The pharmacokinetics of pyrazinamide and ethambutol were similar in both groups. Mild (grade 1 or 2) hepatotoxicity was more common in the higher-dose group (46 versus 20%; P = 0.054), but no patient developed severe hepatotoxicity. Increasing the rifampin dose was associated with a more than dose-proportional increase in the mean AUC(0-24) and C(max) of rifampin without affecting the incidence of serious adverse effects. Follow-up studies are warranted to assess whether high-dose rifampin may enable shortening of TB treatment.

Biological evaluation of pyrazinamide liposomes for treatment of Mycobacterium tuberculosis

Pyrazinamide liposomes were prepared employing the phospholipid molar ratios; dipalmitoyl phosphatidyl choline (7):cholesterol (2) neutral and dipalmitoyl phosphatidyl choline (7):cholesterol (2):dicetyl phosphate (1) negatively charged. Swelling at 52 degrees C led to higher trapping efficiencies. An optimum sterilizing dose of 25 kGy was exhibited by gamma (gamma)-irradiation. Neutral pyrazinamide liposomes (7:2), swollen for 24 h, were employed in biological evaluation for treatment of mice infected by Mycobacterium tuberculosis. Liposomal pyrazinamide could effect highly significant reduction in bacterial counts (colony forming units/g lung), 10, 20 and 30 days after the last treatment dose. Histopathological examination of mice lungs showed highest severity of infection in drug-free liposomes (control) group > pyrazinamide liposomes > free pyrazinamide 6 days/week. The results indicate high therapeutic efficacy of pyrazinamide liposomes, injected twice weekly, in treatment of M. tuberculosis in mice.

Modification to improve efficiency of sampling schedules for BA/BE testing of FDC anti-tuberculosis drugs

SETTING

The assessment of rifampicin (RMP) containing fixed-dose combination (FDC) formulations using in vivo bioequivalence testing is widely accepted. It would be advantageous for both the drug regulatory authorities and drug manufacturers, for optimum minimum blood testing time intervals that encompass all anti-tuberculosis active constituents in the FDC to be established.

OBJECTIVE

To determine the optimum blood sampling schedule for testing novel FDC anti-tuberculosis drugs, isoniazid, RMP, pyrazinamide and ethambutol

DESIGN

The results of 12 different single-dose, two-way cross-over designs are presented. The studies determined the bioavailability and bioequivalence of RMP-containing FDCs, and conformed with the requirements of the South African national drug regulatory authority for each of the active constituents.

RESULTS

The pharmacokinetic parameters to determine bioavailability and the Hauschke method to determine bioequivalence revealed that a six-point time protocol, namely 0, 1, 2, 4, 6 and 8 h, provides a good approximation of the area under the curve, and that an 11-point time protocol of 0, 0.25, 0.5, 1, 1.5, 2, 2.5, 3, 4, 6 and 8 h provided information comparable to the conventional 15 time-points for FDCs containing up to four drugs.

CONCLUSION

The findings provide concrete economic benefit and convenience for quality assurance testing of existing and novel FDCs.

The Effect of pyrazinamide and rifampicin on isoniazid metabolism in rats

Hepatotoxicity is the main concern during tuberculosis chemotherapy with the first-line drugs isoniazid (INH), rifampicin (RMP) and pyrazinamide (PYR). Since these hepatotoxic events have been associated with INH metabolites, the study aimed to measure the area under curve (AUC) parameter for INH and its metabolites acetylisoniazid (AcINH), hydrazine (Hz) and acetylhydrazine (AcHz), when groups of rats were pre-treated for 21 days with INH alone or in combination with RMP and/or PYR, in the following amounts per kg body weight: INH 100 mg; INH 100 mg + RMP 100 mg; INH 100 mg + PYR 350 mg; INH 100 mg + PYR 350 mg + RMP 100 mg. It was found that co-administration of RMP, PYR and RMP + PYR caused a significant decrease in the AUC for INH. Co-administration of PYR was the only treatment that caused a significant increase in the AUC for Hz and a decrease in the AUC for its acetylated product AcHz. The AUC for AcINH was not significantly altered in any experimental group. In conclusion, the increased metabolism of INH in all the drug combinations and the significantly higher production of Hz in the group INH + PYR might be linked with exacerbated hepatotoxic effects of these drug associations.

Alginate nanoparticles as antituberculosis drug carriers: formulation development, pharmacokinetics and therapeutic potential

BACKGROUND

Reduction in the dosing frequency of antituberculosis drugs (ATDs) by applying drug delivery technology has the potential to improve the patient compliance in tuberculosis (TB). Alginate (a natural polymer) based nanoparticulate delivery system was developed for frontline ATDs (rifampicin, isoniazid, pyrazinamide and ethambutol).

METHODS

Alginate nanoparticles were prepared by the controlled cation induced gelification method and administered orally to mice. The drug levels were analysed by high performance liquid chromatography (HPLC) in plasma/tissues. The therapeutic efficacy was evaluated in M. tuberculosis H37Rv infected mice.

RESULTS

High drug encapsulation efficiency was achieved in alginate nanoparticles, ranging from 70%-90%. A single oral dose resulted in therapeutic drug concentrations in the plasma for 7-11 days and in the organs (lungs, liver and spleen) for 15 days. In comparison to free drugs (which were cleared from plasma/organs within 12-24 h), there was a significant enhancement in the relative bioavailability of encapsulated drugs. In TB-infected mice three oral doses of the formulation spaced 15 days apart resulted in complete bacterial clearance from the organs, compared to 45 conventional doses of orally administered free drugs.

CONCLUSIONS

Alginate nanoparticles appear to have the potential for intermittent therapy of TB.

Determinants of rifampin, isoniazid, pyrazinamide, and ethambutol pharmacokinetics in a cohort of tuberculosis patients

Evaluation of sources of pharmacokinetic variation can facilitate optimization of tuberculosis treatment regimens by identification of avoidable sources of variation and of risk factors for low or high drug concentrations in patients. Our objective was to describe the pharmacokinetics of rifampin, isoniazid, pyrazinamide, and ethambutol in a cohort of tuberculosis patients established on first-line treatment regimens and to evaluate the determinants of pharmacokinetic variation. Plasma concentration-time profiles were determined for each of the drugs in 142 patients with drug-sensitive pulmonary tuberculosis after 2 months of daily treatment in hospital. Pharmacokinetic measures were described by noncompartmental analysis. Multiple linear regression was used to evaluate the patient and the treatment factors associated with variation of the area under the concentration-time curve from 0 to 8 h. Several factors independently associated with variations in antituberculosis drug concentrations were identified: human immunodeficiency virus infection was associated with 39% and 27% reductions for rifampin and ethambutol, respectively; formulation factors were determinants of rifampin and isoniazid bioavailability; female patients had increased rifampin and isoniazid concentrations but reduced ethambutol concentrations; older patients had higher levels of isoniazid and ethambutol; patients with a history of previous antituberculosis treatment had lower ethambutol concentrations; and the dose per kilogram of body weight was associated with the concentrations of all four agents. Further studies are required to assess the implications of variations in antituberculosis drug concentrations for efficacy and safety before decisions are made to change the dosing strategy in patients at risk.

Variability in the population pharmacokinetics of pyrazinamide in South African tuberculosis patients

OBJECTIVE

This study was designed to characterize the population pharmacokinetics of pyrazinamide in South African pulmonary tuberculosis patients, with special reference to interindividual and interoccasional variability (IIV and IOV, respectively).

METHODS

Concentration-time measurements obtained from 227 patients receiving oral doses of pyrazinamide were pooled to create a dataset containing 3,092 data points spanning multiple dosing occasions. The software program NONMEM was used to analyze the data.

RESULTS

A one-compartment model with first-order absorption, including a zero-order component describing release from formulation, and first-order elimination best described the data. The absorption rate constant was estimated to be bimodally distributed between two distinct subgroups, fast and slow, in approximately even proportion. Absorption rate was threefold greater in fast absorbers (3.56 h(-1)) in comparison to slow absorbers (1.25 h(-1)). Typical values of oral clearance and apparent volume of distribution were estimated as 3.42 L h(-1) and 29.2 l, respectively. IOV was supported in oral clearance (0.0238, variance) and absorption rate (0.623, variance). The duration of zero-order absorption was estimated as 0.290 h, and was quite variable between patients (0.957, variance).

CONCLUSION

The absorption of pyrazinamide in the studied population was highly variable and two separate subpopulations were identified. IOV accounted for a proportion of the variability in clearance and the absorption rate constant.

Pharmacokinetic and pharmacodynamic behaviour of antitubercular drugs encapsulated in alginate nanoparticles at two doses

This study was designed to evaluate the pharmacokinetics and tissue distribution of free and alginate-encapsulated antitubercular drugs in mice at different doses. Alginate nanoparticles encapsulating isoniazid (INH), rifampicin (RIF), pyrazinamide (PZA) and ethambutol (EMB) were prepared by controlled cation-induced gelification of alginate. The formulation was orally administered to mice at two dose levels (D1 and D2). A comparison was made in mice receiving free drugs at equivalent doses. Drugs were analysed by high performance liquid chromatography (HPLC). The average size of alginate nanoparticles was found to be 235.5+/-0.0 nm with a polydispersity index of 0.44; drug encapsulation was 70-90% for INH and PZA, 80-90% for RIF and 88-95% for EMB. In the free drug groups, plasma levels of RIF and INH were higher and PZA and EMB levels were lower in the D1 group (per body surface area of mice) compared with the D2 group (recommended human dose). The plasma drug levels of all drugs were higher in the D1 encapsulated group compared with D2, resulting in higher values of area under the plasma drug concentration-time curve (AUC(0-infinity)). The relative bioavailabilities of all drugs encapsulated in alginate nanoparticles were significantly higher compared with free drugs. Drug levels were maintained at or above the minimum inhibitory concentration (MIC(90)) until Day 15 in organs after administration of encapsulated drugs, whilst free drugs stayed at or above the MIC(90) up to Day 1 only irrespective of dose. The levels of drugs in various organs remained above the MIC at both doses for equal periods, demonstrating their equiefficiency. Alginate nanoparticles hold great potential in reducing dosing frequency of antitubercular drugs.

Potent twice-weekly rifapentine-containing regimens in murine tuberculosis

RATIONALE

Recent studies have demonstrated that intermittent administration of rifamycin-based regimens results in higher rates of tuberculosis relapse and treatment failure compared with daily therapy. Twice-weekly treatment with rifampin, isoniazid, and pyrazinamide may be improved by increasing Mycobacterium tuberculosis exposure to rifamycin by substituting rifapentine for rifampin.

METHODS

To test this hypothesis, we compared the activities of standard daily and twice-weekly rifampin plus isoniazid-based regimens to those of twice-weekly rifapentine plus isoniazid- or moxifloxacin-containing regimens in the murine model of tuberculosis. Relapse rates were assessed after 4, 5, and 6 mo of treatment to assess stable cure. Single- and multiple-dose pharmacokinetics of rifampin and rifapentine were also determined.

RESULTS

After 2 mo of treatment, twice-weekly therapy with rifapentine (15 or 20 mg/kg), moxifloxacin, and pyrazinamide was significantly more active than standard daily or twice-weekly therapy with rifampin, isoniazid, and pyrazinamide. Stable cure was achieved after 4 mo of twice-weekly rifapentine plus isoniazid- or moxifloxacin-containing therapy, but only after 6 mo of standard daily therapy. Twice-weekly rifapentine (15 mg/kg) displayed more favorable pharmacodynamics than did daily rifampin (10 mg/kg).

CONCLUSIONS

By virtue of the enhanced rifamycin exposure, twice-weekly regimens containing rifapentine (15 or 20 mg/kg) may permit shortening the current treatment duration by 2 mo. Such regimens warrant clinical investigation.

Low levels of pyrazinamide and ethambutol in children with tuberculosis and impact of age, nutritional status, and human immunodeficiency virus infection

Recent pharmacokinetic studies that included children found that serum drug levels were low compared to those of adults for whom the same dosages were used. This study aimed to characterize the pharmacokinetics of pyrazinamide and ethambutol in Malawian children and to examine the impact of age, nutritional status, and human immunodeficiency virus (HIV) infection. We conducted a pharmacokinetic study of children treated for tuberculosis with thrice-weekly pyrazinamide (n = 27; mean age, 5.7 years) and of a separate group of children treated with thrice-weekly ethambutol (n = 18; mean age, 5.5 years) as portions of tablets according to national guidelines. Malnutrition and HIV infection were common in both groups. Blood samples were taken just prior to oral administration of the first dose, and subsequent samples were taken at intervals of 2, 3, 4, 7, 24, and 48 h after drug administration. Serum drug levels were low in all children for both drugs; in almost all cases, the maximum concentration of the drug in serum (Cmax) failed to reach the MIC for Mycobacterium tuberculosis. The Cmax of pyrazinamide was significantly lower in younger children (<5 years) than in older children. The Cmax of pyrazinamide was also lower for HIV-infected children and children with severe malnutrition, but these differences did not reach statistical significance. No differences were found for ethambutol in relation to age, HIV infection, or malnutrition, but the Cmax was <2 mg/liter in all cases. Studies of pharmacokinetic parameters and clinical outcomes obtained by using higher dosages of drugs for treatment of childhood tuberculosis are needed, and recommended dosages may need to be increased.

Inhalable alginate nanoparticles as antitubercular drug carriers against experimental tuberculosis

Pharmacokinetic and chemotherapeutic studies have been carried out with aerosolised alginate nanoparticles encapsulating isoniazid (INH), rifampicin (RIF) and pyrazinamide (PZA). The nanoparticles were prepared by cation-induced gelification of alginate and were 235.5 +/- 0 nm in size, with drug encapsulation efficiencies of 70-90% for INH and PZA and 80-90% for RIF. The majority of particles (80.5%) were in the respirable range, with mass median aerodynamic diameter of 1.1 +/- 0.4 microm and geometric standard deviation of 1.71 +/- 0.1 microm. The relative bioavailabilities of all drugs encapsulated in alginate nanoparticles were significantly higher compared with oral free drugs. All drugs were detected in organs (lungs, liver and spleen) above the minimum inhibitory concentration until 15 days post nebulisation, whilst free drugs stayed up to day 1. The chemotherapeutic efficacy of three doses of drug-loaded alginate nanoparticles nebulised 15 days apart was comparable with 45 daily doses of oral free drugs. Thus, inhalable alginate nanoparticles can serve as an ideal carrier for the controlled release of antitubercular drugs.

Population pharmacokinetics of pyrazinamide in elephants

This study was undertaken to characterize the population pharmacokinetics (PK), therapeutic dose, and preferred route of administration for pyrazinamide (PZA) in elephants. Twenty-three African (Loxodonta africana) and Asian (Elephas maximus) elephants infected with or in contact with others culture positive for Mycobacterium tuberculosis were dosed under treatment conditions. PZA was dosed daily at 20-30 mg/kg via oral (fasting or nonfasting state) or rectal (enema or suppository) administration. Blood samples were collected 0-24 h postdose. Population PK was estimated using nonlinear mixed effect modeling. Drug absorption was rapid with T(max) at or before 2 h regardless of the method of drug administration. C(max) at a mean dose of 25.6 (+/-4.6) mg/kg was 19.6 (+/-9.5 microg/mL) for PZA given orally under fasting conditions. Under nonfasting conditions at a mean dose of 26.1 +/- 4.2 mg/kg, C(max) was 25% (4.87 +/- 4.89 microg/mL) and area under concentration curve (AUC) was 30% of the values observed under fasting conditions. Mean rectal dose of 32.6 +/- 15.2 mg/kg yielded C(max) of 12.3 +/- 6.3 microg/mL, but comparable AUC to PZA administered orally while fasting. Both oral and rectal administration of PZA appeared to be acceptable and oral dosing is preferred because of the higher C(max) and lower inter-subject variability. A starting dose of 30 mg/kg is recommended with drug monitoring between 1 and 2 h postdose. Higher doses may be required if the achieved C(max) values are below the recommended 20-50 microg/mL range.

Oral solid lipid nanoparticle-based antitubercular chemotherapy

The present study was planned to evaluate the chemotherapeutic potential of oral solid lipid nanoparticles (SLNs) incorporating rifampicin, isoniazid and pyrazinamide against experimental tuberculosis. The SLNs were prepared by the "emulsion solvent diffusion" technique with an encapsulation efficiency of 51+/-5% for rifampicin, 45+/-4% for isoniazid and 41+/-4% for pyrazinamide. Following a single oral administration to mice, therapeutic drug concentrations were maintained in the plasma for 8 days and in the organs (lungs, liver and spleen) for 10 days whereas free drugs were cleared by 1-2 days. In M. tuberculosis H37Rv infected mice, no tubercle bacilli could be detected in the lungs/spleen after 5 oral doses of drug loaded SLNs administered at every 10th day whereas 46 daily doses of oral free drugs were required to obtain an equivalent therapeutic benefit. Thus, SLN based antitubercular drug therapy forms a sound basis for reducing dosing frequency and improving patient compliance for better management of tuberculosis.

Serum concentrations of antimycobacterial drugs in patients with pulmonary tuberculosis in Botswana

BACKGROUND

We conducted a pharmacokinetic study of antimycobacterial drugs involving a cohort of patients with pulmonary tuberculosis (TB) in Gaborone, Botswana, to assess the prevalence of and risk factors for low drug concentrations in serum.

METHODS

Adults participated if they had a history of cough > or =2 weeks, had abnormal chest radiograph findings, consented to testing for human immunodeficiency virus (HIV), had sputum cultures positive for Mycobacterium tuberculosis, and were receiving antituberculous therapy for >7 days. Observed maximum serum concentrations were compared with published normal ranges. RESULTS. Of 91 patients enrolled, 89 (98%) were outpatients, and 59 (68%) of 87 patients tested had HIV infection. The following numbers of patients had low serum concentrations of the following drugs: isoniazid, 27 (30%) of 90; rifampin, 71 (78%) of 91; ethambutol, 37 (41%) of 91; and pyrazinamide, 1 (1%) of 91. Low serum concentrations of both isoniazid and rifampin occurred in 23 (26%) of 90 patients. Low serum concentrations of rifampin were found in both HIV-infected and non-HIV-infected patients, and such patients were less likely to have >4 weeks of symptoms, more likely to have lymphadenopathy, and more likely to have low serum albumin levels (P<.05 for all). The associations with noncavitary pulmonary disease (P=.12) and HIV infection (P=.07) did not reach statistical significance. Delayed absorption was most common with ethambutol, followed by rifampin.

CONCLUSIONS

These data, predominantly from HIV-infected patients with TB, suggest that low isoniazid, rifampin, and ethambutol concentrations are common in Botswana. In contrast, pyrazinamide usually is well absorbed.

Solid lipid particle-based inhalable sustained drug delivery system against experimental tuberculosis

The present study was planned to evaluate the chemotherapeutic potential of nebulized solid lipid particles (SLPs) incorporating rifampicin, isoniazid and pyrazinamide against experimental tuberculosis. The SLPs prepared by the "emulsion solvent diffusion" technique possessed a favourable mass median aerodynamic diameter suitable for bronchoalveolar drug delivery. Following a single nebulization to guinea pigs, therapeutic drug concentrations were maintained in the plasma for 5 days and in the organs (lungs, liver and spleen) for 7 days whereas free drugs were cleared by 1-2 days. The mean residence time and drug bioavailability were improved several-fold in the case of drug-loaded SLPs. A similar pharmacokinetic profile was observed in Mycobacterium tuberculosis-infected guinea pigs. On nebulization of drug-loaded SLPs to infected guinea pigs at every 7th day, no tubercle bacilli could be detected in the lungs/spleen after 7 doses of treatment whereas 46 daily doses of orally administered drugs were required to obtain an equivalent therapeutic benefit. Further, there was no evidence of any biochemical hepatotoxicity. Thus, nebulization of SLP-based antitubercular drugs forms a sound basis for improving drug bioavailability and reducing the dosing frequency for better management of pulmonary tuberculosis.

Decreased bioavailability of rifampin and other antituberculosis drugs in patients with advanced human immunodeficiency virus disease

We evaluated the effects of human immunodeficiency virus (HIV) disease on pharmacokinetics of antituberculosis medications by measuring concentrations of isoniazid and rifampin in blood and of pyrazinamide and ethambutol in urine. Peak concentration and exposure were reduced for rifampin, and rapid acetylators of isoniazid had lower drug levels. HIV and HIV-tuberculosis patients who have diarrhea and cryptosporidial infection exhibit decreased bioavailability of antituberculosis drugs.

Penetration of isoniazid, rifampicin and pyrazinamide in tuberculous pleural effusion and psoas abscess

SETTING

Tuberculosis Centre, University Medical Centre, Groningen, The Netherlands.

OBJECTIVES

To study intralesional concentrations of isoniazid (INH), rifampicin (RMP) and pyrazinamide (PZA) in tuberculous pleural effusions and psoas abscesses, and to compare these to reference serum values and minimal inhibitory concentration (MIC).

DESIGN

Intralesional concentrations were measured 2 h after drug administration (six pleural effusions, 10 psoas abscesses).

RESULTS

A wide range of concentrations was found for pleural effusions and psoas abscesses. Concentrations were below MIC values in none of 15 patients for INH, in two of 13 for RMP, and in eight of nine for PZA. The Cmax:MIC ratio was always >4 for INH, in four of 13 for RMP, and in none of nine for PZA. In 5/8 patients receiving all three drugs, both RMP and PZA had Cmax:MIC ratios <4, indicating sub-therapeutic drug levels.

CONCLUSION

Penetration of INH was always sufficient, penetration of RMP mostly below the desired ratio, and for PZA on average 10 times too low. Five of eight patients on all three drugs had Cmax:MIC ratios <4. This indicates intralesional sub-therapeutic drug levels for RMP and PZA, and local monotherapy with INH. This could induce drug resistance. Drainage as additional therapy seems indicated.

Comparative bioavailability of rifampicin, isoniazid and pyrazinamide from a four drug fixed dose combination with separate formulations at the same dose levels

Fixed dose combination (FDC) formulations became popular in the treatment of tuberculosis (TB) because of the better patient compliance, reduced risk of monotherapy and emergence of drug resistance in contrast to treatment with separate formulations of two to four first-line drugs. However, its successful implementation in national programs is limited by probable bioinequivalency of rifampicin if present in FDC form. In this regard, World Health Organization (WHO) and International Union Against Tuberculosis and Lung Disease (IUATLD) recommend FDCs only of proven bioavailability. Hence, bioequivalence study of four drug FDC tablet was conducted using 22 healthy male volunteers according to WHO recommended protocol to determine bioavailability of rifampicin, isoniazid and pyrazinamide compared to standard separate combination at the same dose level. The study was designed as two period, two treatment crossover experiment with a washout period of 1 week. Bioequivalence of rifampicin was estimated by plasma and urinary method for both rifampicin and its active metabolite, des-acetyl rifampicin whereas isoniazid and pyrazinamide were estimated from plasma. Mean concentration time profiles and all the pharmacokinetic parameters of rifampicin, isoniazid and pyrazinamide from FDC tablet were comparable to individual formulations and passed the bioequivalence test with power of the test above 95%. Further, bioequivalence of both rifampicin and isoniazid shows that in vitro interaction of rifampicin and isoniazid is clinically insignificant. Thus, it was concluded that FDC formulation is bioequivalent for rifampicin, isoniazid and pyrazinamide and ensures the successful treatment of TB without compromising therapeutic efficacy of any of these components of anti-TB therapy.

The Clinical Pharmacokinetics of Pyrazinamide in HIV‐Infected Persons with Tuberculosis

The pharmacokinetics of pyrazinamide (PZA) in patients with human immunodeficiency virus (HIV)-related tuberculosis are incompletely characterized. Serum PZA concentrations were determined at 2, 6, and 10 h after dosing in 48 subjects with HIV-related tuberculosis. Estimates of drug exposure using 2-h concentrations and 2- and 3-time point estimates of area under time-concentration curves (AUCs) were compared. For daily dosing, 2-h concentrations less than low and very low literature-defined cut points (i.e., 20 and 10 mg/L) were noted for 2 subjects (4%) and 1 subject (2%), respectively. For intermittent PZA dosing, 1 subject (4%) had a 2-h concentration that was less than the low cut point (25 mg/L). Correlations between 2-h concentration and AUC estimates based on 2- or 3-time point concentration determinations were strong. In HIV-infected persons receiving antituberculosis regimens containing PZA, lower-than-expected 2-h concentrations are uncommon. For therapeutic monitoring of PZA drug exposure, determination of a 2-h postdose concentration appears as reliable as 2- or 3-time point estimates of the AUC for PZA.

Evaluation of bioequivalence of isoniazid and pyrazinamide in three and four drugs fixed dose combinations using WHO simplified protocol

The reliable supply of quality drugs in the form of fixed dose combination (FDC) is an essential part of tuberculosis treatment. The objective of this investigation was to evaluate whether the World Health Organization (WHO) simplified screening protocol for the bioequivalence assessment of rifampicin can be used for the evaluation of other components of FDC so as to ensure the bioavailability of all drugs at tissue site. These bioequivalence studies were conducted on 20 and 22 healthy male volunteers for evaluation of three and four drugs FDC formulations, respectively. Both studies were conducted as randomized, open, crossover trials and sampling schedule was upto 8h according to WHO recommended protocol for evaluation of rifampicin bioequivalence. The bioequivalence of isoniazid and pyrazinamide were estimated using AUC(0-8), AUC(0-alpha), and C(max). FDC formulation was considered bioequivalent to separate formulations for isoniazid and pyrazinamide if bioequivalence limit fall in between 0.80 and 1.25. Bioequivalence estimates of AUC(0-8) and AUC(0-alpha) for isoniazid and all the three pharmacokinetic measures of pyrazinamide were within the acceptable limits, whereas C(max) of isoniazid from four drugs FDC was outside the limit when evaluated by two-way ANOVA. After evaluation of isoniazid and pyrazinamide based on their pharmacokinetics, it was found that C(max) is being affected by limited sampling time points of WHO protocol. Further, AUC was a robust parameter unaffected by sampling schedule adopted. The WHO simplified protocol for assessment of rifampicin is also suitable for evaluating bioequivalence of isoniazid and pyrazinamide from FDC formulations. However, for comparison of rate of absorption by means of C(max), careful evaluation of concentration-time profile along with pharmacokinetics is necessary before final judgment.

Chemotherapeutic potential of orally administered poly(lactide-co-glycolide) microparticles containing isoniazid, rifampin, and pyrazinamide against experimental tuberculosis

Poly(lactide-co-glycolide) (PLG) microspheres (diameter, less than 3 microm) containing isoniazid, rifampin, and pyrazinamide were used in a sustained oral drug delivery system to treat murine tuberculosis. Drug levels above the MIC were observed up to 72 h in plasma and for 9 days in various organs. Relative bioavailability of encapsulated drugs was greater than that of free drugs. Chemotherapy results showed better or equivalent clearance of bacilli in the PLG-drug-administered group (weekly) than with free drugs (daily).

Effect of peritoneal dialysis on plasma and peritoneal fluid concentrations of isoniazid, pyrazinamide, and rifampin

OBJECTIVE

This study was performed to elucidate the pharmacokinetic profiles of antimycobacterial regimens for peritoneal dialysis patients.

PATIENTS

Nine patients on maintenance continuous ambulatory peritoneal dialysis (CAPD) were included in this study.

METHODS

After administering a conventional oral dose of antituberculosis medications, we measured plasma and peritoneal fluid concentrations of isoniazid by fluorometry, and rifampin and pyrazinamide by high performance liquid chromatography. The assay data were subjected to pharmacokinetic analysis.

RESULTS

Average peak plasma concentrations of isoniazid, rifampin, and pyrazinamide were 3.3 mg/L, 6.5 mg/L, and 30.9 mg/L, respectively, all of which much exceed the minimum inhibitory concentration (MIC) for Mycobacterium tuberculosis. Peritoneal fluid concentrations of isoniazid and pyrazinamide were maintained well above the MICs for M. tuberculosis; however, peritoneal fluid concentration of rifampin was below the therapeutic range most of the time.

CONCLUSION

For the treatment of systemic or pulmonary tuberculosis in CAPD patients, no dose adjustments are required for isoniazid, rifampin, or pyrazinamide. On the contrary, for the treatment of tuberculous peritonitis, oral rifampin therapy is not expected to be effective because of its low peritoneal fluid concentration.

Alginate-based oral drug delivery system for tuberculosis: pharmacokinetics and therapeutic effects

Alginate microparticles were developed as oral sustained delivery carriers for antitubercular drugs in order to improve patient compliance. In the present study, pharmacokinetics and therapeutic effects of alginate microparticle encapsulated antitubercular drugs, i.e. isoniazid, rifampicin and pyrazinamide were examined in guinea pigs. Alginate microparticles containing antitubercular drugs were evaluated for in vitro and in vivo release profiles. These microparticles exhibited sustained release of isoniazid, rifampicin and pyrazinamide for 3-5 days in plasma and up to 9 days in organs. Peak plasma concentration (Cmax), Tmax, elimination half-life (t1/2e) and AUC0- infinity of alginate drugs were significantly higher than those of free drugs. The encapsulation of drug in alginate microparticles resulted in up to a nine-fold increase in relative bioavailability compared with free drugs. Chemotherapeutic efficacy of alginate drug microspheres against experimental tuberculosis showed no detectable cfu values at 1:100 and 1:1000 dilutions of spleen and lung homogenates. Histopathological studies further substantiated these observations, thus suggesting that application of alginate-encapsulated drugs could be useful in the effective treatment of tuberculosis.

A pilot stability study on four-drug fixed-dose combination anti-tuberculosis products

A pilot stability study was carried out on four fixed-dose combination anti-tuberculosis products at 40 degrees C and 75% RH. The strip-packed products were stable, while the blister-packed products showed both physical and chemical changes. The products in unpacked conditions showed severe (approximately 60%) decomposition of rifampicin and extensive physical changes. The main decomposition product in the solid state was isonicotinyl hydrazone of 3-formylrifamycin and isoniazid. It is suggested that attention should be paid to the detection and quantitation of this product in the marketed formulations. The packing material used in the manufacture of FDC products should also be of the highest quality.