Plasma drug concentrations of 4-drug fixed-dose combination regimen and its efficacy for treatment of pulmonary tuberculosis under National Tuberculosis Elimination Programme: A prospective pilot study

•Suboptimal plasma levels (C2h post dose) of isoniazid (H), rifampicin (R) and ethambutol (E) were less frequently observed in pulmonary tuberculosis patients administering daily regimen with 4-drug fixed-dose combination under National TB Elimination Programme.•Suboptimal concentrations of isoniazid and rifampicin were frequently observed in males compared to females.•All the patients were cured despite of low first-line TB plasma levels but the chance of development of MDR-TB in long run cannot be ruled out in those patients having concurrent suboptimal plasma levels of isoniazid and rifampicin.•Pyrazinamide plasma levels were optimal and plausibly contributed to favourable outcome. Requires further study.