Minimal inhibitory concentration of isoniazid in isoniazid-resistant Mycobacterium tuberculosis isolates from children

The aim of the study presented here was to determine the minimal inhibitory concentration of isoniazid for strains of isoniazid-resistant or multidrug-resistant Mycobacterium tuberculosis isolated from children in the Western Cape Province of South Africa. During the period March 2003–October 2005, 45 INH-resistant M. tuberculosis isolates (21 also rifampicin-resistant) were cultured from children less than 13 years of age. Drug susceptibility testing by the radiometric BACTEC 460 method found 11 isolates resistant at 0.1 μg/ml, 27 resistant at 0.2 μg/ml, and seven resistant at ≥5 μg/ml. Thus, the minimal inhibitory concentration of isoniazid for more than 80% of the isoniazid-resistant strains isolated from children in this study was relatively low and could be exceeded by high-dose (15–20 mg/kg) isoniazid regimens.