EARLY BACTERICIDAL ACTIVITY OF ETHAMBUTOL, PYRAZINAMIDE AND THE FIXEDCOMBINATION OF ISONIAZID, RIFAMPICIN AND PYRAZINAMIDE (RIFATER) IN PATIENTS WITH PULMONARY TUBERCULOSIS

The early bactericidal activity (EBA) of ethambutol, pyrazinamide and the fixed combination of isoniazid, rifampicin and pyrazinamide (Rifat er: Mer National) was evaluated in patients with pulmonary tuberculosi s who were sputum-positive on microscopy for acid-fast bacilli. Twenty -eight patients (mean age 33 years and weight 51 kg on average; range 40 - 59 kg) were studied, The fall in viable counts of Mycobacterium t uberculosis in sputum collections during the 2 days following the star t of treatment was estimated from counts of colony-forming units (CFUs ) of M. tuberculosis per ml of sputum cultured on selective 7H10 agar medium, The EBA for ethambutol determined in 9 patients was 0.245 +/- 0.046, log(10) CFU/ml sputum/day, that for pyrazinamide was 0.003 +/- 0.014 log(10) CFU/ml sputum/day and that for Rifater 0.558 +/- 0.054 l og(10) CFU/ml sputum/day, The results obtained are similar to those re ported in a previous study of the first 2 days of treatment, but in sm aller numbers of patients, and confirm the moderate EBA of ethambutol while pyrazinamide is again shown to have very little EBA, Rifater has a marked EBA which may be due mainly to the action of isoniazid. This methodology may be valuable in the rapid evaluation of the bactericid al activity of new antituberculosis agents and the comparison of diffe rent dose sizes of agents of the same class.