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Monday 21 May 2012

Levothyroxine sodium

Class: Thyroid Hormone
Mech.: Sodium salt of T4. T3/T4 synergize w/GH effects, increase BMR, potentiate catecholamine effects on heart, promote lipolysis, and decrease serum cholesterol.

Absorption: Incomplete oral absorption—30-40% recovered in stool.
Dist.: Poor placental transfer → okay for pregnant E. Little in milk (use cautiously).
Metab.: Hepatic conjug. w/glucuronic & sulfuric acids. Peripheral deiodination to T3.
Excretion, t_: Bile; some lost in stool due to enterohepatic circ. 6-7 d.
Toxicity/S.E.s: Salicylates and dicumarol compete for albumin binding sites → marked increase of free levels.

Utility: Treat hypothyroidism and goiter (not due to iodine deficiency or hyperthyroidism).
Special Features: 200-300 μg/d. 1/4 the potency of liothyronine sodium, but same efficacy.

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