PHAR 441 Lecture Notes - Lecture 7: Hepatotoxicity, Thyroid Storm, Aplasia
14 Oct 2016
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Goals of therapy: reverse signs/symptoms of hypothyroidism, normalize tsh and ft4, avoid over-treatment. Levothyroxine sodium (synthetic t4) is the treatment of choice, regardless of the cause. T4 is converted to t3 normally, t3 levels will be normalized with tx. <50 y/o, healthy: can start with full replacement doses. Elderly/cad: start with lower doses and gradually increase to avoid precipitating angina or arrhythmias. Long t1/2 (7 days) once daily administration. Takes 5-6 weeks for steady state to be reached. 60-80% of administered dose is absorbed in the small intestine. Narrow therapeutic index easy to over-treat over-treatment is associated with: Low tsh in the subnormal range (n = 0. 5-5 mu/l) Reduced bone density increased risk of fracture if tsh is <0. 03 mu/l. Initially tsh levels measured every 6-8 weeks until normalized, then every 6-12 months. Ca2+ supplements, iron, cholestyramine binds t4 and prevents absorption. Rifampin, phenytoin induce hepatic microsomal enzymes and increase t4 breakdown.
