| Whatever the type of hypothyroidism, the drug of choice is L-T4 rather than other preparations, either T3, T4/T3 mixtures, or thyroid extracts. T4 treatment has the advantage of mimicking natural predominant T4 secretion, with extrathyroidal T4-to-T3 conversion generating the appropriate amounts of T3. Stability of T4 blood level makes therapeutic dosage adjustments more meaningful and the long half-life of T4 makes it possibile for the total daily dose to be taken as a single dose. The mean absorption of T4 conditionned in tablets has been estimated to be 75 %. Malabsorption of T4 is very rare except in patients with short-bowel syndrome or liver cirrhosis, or when T4 is administered concomitantly with cholestyramine or colestipol, aluminium hydroxide, sucralfate, ferrous sulfate and in infants fed soybean formula. |
