INHA and tuberculosis: Isoniazid (INH, H) resistance in Mycobacterium tuberculosis (MTB) is likely a natural phenomenon due to frequent spontaneous mutations, especially at codon 315 of the katG gene resulting in moderate- to high-level resistance and the c-15t mutation in the inhA promoter region resulting in low-level resistance.1,2 INH resistance is the most common TB resistance pattern, accounting for over 1 million new cases annually.3,4 Furthermore, INH monoresistance is the most common TB monoresistance pattern.5,6