The antimicrobial spectrum of ethionamide includes "M. tuberculosis", "M. bovis" and "M. segmatis". It also is used rarely against infections with "M. leprae" and other nontuberculous mycobacteria such as "M. avium" and "M. kansasii." While working in a similar manner to isoniazid, cross resistance is only seen in 13% of strains, since they are both prodrugs but activated by different pathways. Resistance can emerge from mutations in ethA, which is needed to activate the drug, or ethR, which can be overexpressed to repress ethA. Mutations in inhA or the promoter of inhA can also lead to resistance through changing the binding site or overexpression.