Levothyroxine Barbiturates

THYROID HORMONES ANTIEPILEPTICS-BARBITURATES, CARBA-MAZEPINE, PHENYTOIN 1 levothyroxine levels Induction of metabolism Monitor TFTs regularly and consider T dose of levothyroxine... 

Clinically important, potentially hazardous interactions with allopurinol, amiodarone, amobarbital, anabolic steroids, anti-thyroid agents, aprobarbital, aspirin, barbiturates, bivalirudin, butabarbital, butalbital, cimetidine, clofibrate, clopidogrel, cyclosporine, delavirdine, disulfiram, fenofibrate, fluconazole, gemfibrozil, glutethimide, imatinib, itraconazole, ketoconazole, levothyroxine, liothyronine, mephobarbital, methimazole, metronidazole, miconazole, penicillins, pentobarbital, phenobarbital, phenylbutazones, piperacillin, prednisone, primidone, propylthiouracil, quinidine, quinine, rifabutin, rifampin, rifapentine, rofecoxib, salicylates, secobarbital, sulfinpyrazone, sulfonamides, testosterone, thyroid, zileuton... 

Despite very clear evidence that both carbamazepine and phenytoin can cause a marked reduction in endogenous serum thyroid hormone levels, the development of clinical hypothyroidism seems to be very rare, and there seems to be only one case on record of an interaction between levothyroxine and phenytoin. There seems to be little reason for avoiding concurrent use, but the outcome should be monitored. Increase the levothyroxine dosage if necessary. Consider also Thyroid hormones + Barbiturates , below. 

An isolated report describes a reduction in the response to levothyroxine when a woman also took a barbiturate. See also Thyroid hormones + Antiepileptics , p.l281. 

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