[Sterilizing activity of the main drugs on the mouse experimental tuberculosis (author's transl)]

In a first experiment mice infected intravenously with 10(6) Mycobacterium tuberculosis were randomly treated either with isoniazid (INH) + rifampicin (RMP) 25 mg/kg or with INH + RMP + pyrazinamide (PZA) or with INH + RMP + PZA + streptomycin (SM). The decrease of the viable counts (CFU) in the lungs was similar with all three regimens. In a second experiment, mice were treated for six months either with INH + RMP 25 mg/kg or INH + RMP 10 mg/kg. After a follow-up of six months, mice were killed and their lungs and spleen cultivated. Positive cultures were obtained in 7.5 p. cent of the mice treated with the high dose of RMP and 36.5 p. cent in the mice treated with the low dose (p less than 0.05). A third experiment demonstrated that, during the first two months of treatment, adding PZA to INH + RMP 10 mg/kg increased significantly the overall effectiveness of INH + RMP 10 mg/kg combination. A fourth experiment demonstrated that after three initial months of INH + RMP 10 mg/kg, RMP alone was as effective as RMP + INH or RMP + INH + PZA. It may be concluded that RMP and PZA are both active on the intracellular population of Mycobacterium tuberculosis and that RMP is the only drug to act on persisting Mycobacterium tuberculosis in extracellular lesions.