<s>[INST] context: Ethionamide (Etm): It is a tuberculostatic drug of moderate efficacy introduced in 1956. It acts on both extra- and intracellular organisms. Atypical mycobacteria are sensitive. Resistance to Etm develops rapidly and some cross resistance with Tzn is seen. It is absorbed orally, distributes all over, including CSF, completely metabolized and has a sho duration of action (t&;h 2-3 hr). Anorexia, nausea, vomiting and abdominal upset are common, especially in Indian patients. Though the recommended dose of Etm is 1 g/day, more than 0.5 g is generally not tolerated. Other side effects are aches and pains, rashes, hepatitis, peripheral or optic neuritis, mental disturbances and impotence. It is seldom used; only in case of resistance to better tolerated drugs. Ethionamide is not considered as 1st line therapy because of its significant gastrointestinal side effects. Ethionamide is thought to prevent organification of iodine in thyroid hormone synthesis as it is structurally related to other thionamides (propylthiouracil and methimazole) . Other MDR TB therapy drug that can cause hypothyroidism is Para-amino salicylic acid (PAS) ESSENTIALS OF MEDICAL PHARMACOLOGY AND WWW.ncbi.nlm.nih.gov/pmc/aicles/PMC4576583/ AUTHOR:K.D.TRIPATHI SIXTH EDITION PAGE NO:743 [/INST] question: Hypothyroidism is caused by which of the following anti-tubercular drug? | options: A: Streptomycin B: Ethionamide C: Thioacetazone D: Ethambutol | answer: B </s>