High Intrapulmonary Rifampicin and Isoniazid Concentrations Are Associated With Rapid Sputum Bacillary Clearance in Patients With Pulmonary Tuberculosis

Background Intrapulmonary pharmacokinetics may better explain response to tuberculosis (TB) treatment than plasma pharmacokinetics. We explored these relationships by modeling bacillary clearance in sputum in adult patients on first-line treatment in Malawi. Methods Bacillary elimination rates (BER) were estimated using linear mixed-effects modelling of serial time-to-positivity in mycobacterial growth indicator tubes for sputum collected during the intensive phase of treatment (weeks 0-8) for microbiologically confirmed TB. Population pharmacokinetic models used plasma and intrapulmonary drug levels at 8 and 16 weeks. Pharmacokinetic-pharmacodynamic relationships were investigated using individual-level measures of drug exposure (area-under-the-concentration-time-curve [AUC] and C-max) for rifampicin, isoniazid, pyrazinamide, and ethambutol, in plasma, epithelial lining fluid, and alveolar cells as covariates in the bacillary elimination models. Results Among 157 participants (58% human immunodeficiency virus [HIV] coinfected), drug exposure in plasma or alveolar cells was not associated with sputum bacillary clearance. Higher peak concentrations (C-max) or exposure (AUC) to rifampicin or isoniazid in epithelial lining fluid was associated with more rapid bacillary elimination and shorter time to sputum negativity. More extensive disease on baseline chest radiograph was associated with slower bacillary elimination. Clinical outcome was captured in 133 participants, with 15 (11%) unfavorable outcomes recorded (recurrent TB, failed treatment, or death). No relationship between BER and late clinical outcome was identified. Conclusions Greater intrapulmonary drug exposure to rifampicin or isoniazid in the epithelial lining fluid was associated with more rapid bacillary clearance. Higher doses of rifampicin and isoniazid may result in sustained high intrapulmonary drug exposure, rapid bacillary clearance, shorter treatment duration and better treatment outcomes. First-line anti-tuberculosis medicines exhibit variable pharmacokinetics. Modeling of serial sputum time-to-positivity data enables estimation of sputum bacillary elimination. Increased intrapulmonary rifampicin or isoniazid exposure (C(max)or area-under-the-concentration-time-curve [AUC]) was associated with rapid bacillary clearance in pulmonary tuberculosis.

Automated summary

This study explores the relationship between intrapulmonary drug levels and sputum bacillary clearance in tuberculosis treatment. The results show that higher drug exposure to rifampicin or isoniazid in the epithelial lining fluid is associated with more rapid bacillary elimination. Higher doses of rifampicin and isoniazid may result in sustained high intrapulmonary drug exposure, rapid bacillary clearance, shorter treatment duration, and better treatment outcomes.