Ethionamide is a second-line agent, structurally similar to isoniazid, used as a second-line therapy for the treatment of multidrug-resistant tuberculosis or active tuberculosis in case of patient intolerance to other drugs. Depending on its the concentration at the infected site and the susceptibility of the infecting organism it may be bacteriostatic or bactericidal. When used alone rapidly develops bacterial resistance. Ethionamide was approved by FDA in 1965 as TRECATOR manufactured by Wyeth Pharmaceuticals Inc. (purchased by Pfizer in 2009). Ethionamide is specific for Mycobacteria and is thought to exert a toxic effect on mycolic acid components of the bacterial cell wall when activated through intermediate S-oxidation by EtaA. Mycolic acid synthesis was shown to be inhibited by ethionamide in the EthA protein-overexpressing mycobacteria,