Abstract

Thyroxine has long been known to be incompletely and variably absorbed from the gut. In one study the proportion of a single dose absorbed varied from 42 to 74%,¹ the rest remaining in the gut possibly bound to undigested protein. Such poor absorption is not in itself clinically important, because the physician allows for it in the dosage he prescribes. What is more important is consistency and reliability of absorption, for if it varies greatly in an individual patient then satisfactory maintenance treatment may become difficult - although the long biological life of thyroxine (the half-life is about 7 days) would tend to prevent major fluctuations.