Isoniazid exposures and acetylator status in Indonesian tuberculous meningitis patients

Optimizing Pyrazinamide Use: A Low-Hanging Fruit in Improving Outcomes with Tuberculous Meningitis? Narrative Review

Tuberculous meningitis (TBM) disables more than a third of its sufferers. Recent research has focused on optimizing the antitubercular regimen, mainly by increasing the dosage of rifampicin. However, pyrazinamide, with higher penetration into the central nervous system, is generally overlooked. We discuss the potential clinical impact of using pyrazinamide throughout antitubercular therapy in TBM, in contrast to only the intensive phase. This approach may improve the treatment outcomes and reduce disability in TBM. We summarize the available data regarding this approach from in vitro studies, clinical cohorts, toxicity data, and baseline resistance rates. Additionally, we discuss the two ongoing clinical trials evaluating this approach.

Pharmacokinetics and pharmacodynamics of high-dose isoniazid for the treatment of rifampicin- or multidrug-resistant tuberculosis in Indonesia

BACKGROUND

Pharmacokinetic data on high-dose isoniazid for the treatment of rifampicin-/multidrug-resistant tuberculosis (RR/MDR-TB) are limited. We aimed to describe the pharmacokinetics of high-dose isoniazid, estimate exposure target attainment, identify predictors of exposures, and explore exposure-response relationships in RR/MDR-TB patients.

METHODS

We performed an observational pharmacokinetic study, with exploratory pharmacokinetic/pharmacodynamic analyses, in Indonesian adults aged 18-65 years treated for pulmonary RR/MDR-TB with standardized regimens containing high-dose isoniazid (10-15 mg/kg/day) for 9-11 months. Intensive pharmacokinetic sampling was performed after ≥2 weeks of treatment. Total plasma drug exposure (AUC0-24) and peak concentration (Cmax) were assessed using non-compartmental analyses. AUC0-24/MIC ratio of 85 and Cmax/MIC ratio of 17.5 were used as exposure targets. Multivariable linear and logistic regression analyses were used to identify predictors of drug exposures and responses, respectively.

RESULTS

We consecutively enrolled 40 patients (median age 37.5 years). The geometric mean isoniazid AUC0-24 and Cmax were 35.4 h·mg/L and 8.5 mg/L, respectively. Lower AUC0-24 and Cmax values were associated (P < 0.05) with non-slow acetylator phenotype, and lower Cmax values were associated with male sex. Of the 26 patients with MIC data, less than 25% achieved the proposed targets for isoniazid AUC0-24/MIC (n = 6/26) and Cmax/MIC (n = 5/26). Lower isoniazid AUC0-24 values were associated with delayed sputum culture conversion (>2 months of treatment) [adjusted OR 0.18 (95% CI 0.04-0.89)].

CONCLUSIONS

Isoniazid exposures below targets were observed in most patients, and certain risk groups for low isoniazid exposures may require dose adjustment. The effect of low isoniazid exposures on delayed culture conversion deserves attention.