Test Details: Ethionamide is a 2nd line drug in the therapy of tuberculosis (TB) used only in combination with other agents and for drug-resistant TB. There is cross resistance between isoniazid and ethionamide, probably because they are activated by different mycobacterial enzymes and therefore can be used together. Ethionamide is currently used only as a secondary agent in the treatment of active tuberculosis, always in combination with other antitubercular agents such as isoniazid, ethambutol, pyrazinamide and/or rifampicin and usually for multidrug resistant mycobacterial infections or in situations where first line agents are contraindicated.