Mutant prevention concentration of isoniazid, rifampicin and rifabutin against Mycobacterium tuberculosis

BACKGROUND: Mutant prevention concentration (MPC) is a new parameter that may be of aid in determining the risk of resistant mutants being selected. METHODS: The MPCs of 224 Mycobacterium tuberculosis clinical isolates were estimated by plating more than 10(10) cells on drug-containing agar and determining the concentration that allowed no colony growth. Antibiotics used were isoniazid, rifampicin and rifabutin. RESULTS: The MPC90 of clinical isolates in our setting is 2.4, 2.2 and 0.4 mg/l for isoniazid, rifampicin and rifabutin, respectively. CONCLUSIONS: Isoniazid and rifampicin are two drugs that present a low risk of selection of resistant mutants when used in monotherapy. However, determination of the MPC of each strain can provide data to minimize this risk and thus enable treatment to be optimized.