The Pharmaceutical Journal
Vol 276 No 7399 p527
6 May 2006

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Acid secretion affects oral thyroxine absorption

Patients with goitre who also have impaired acid secretion need an increased dose of thyroxine, Italian researchers say in The New England Journal of Medicine (2006;354:1787).

They assessed the dose of thyroxine required in 248 patients with multinodular goitre. Of these patients, 53 also had Helicobacter pylori-related gastritis and 60 had atrophic gastritis (with or without H pylori infection). The researchers observed an increase in the need for oral thyroxine in all conditions characterised by impaired gastric acid secretion (ranging from a dose increase of 22 per cent to an increase of 34 per cent).

The researchers make suggestions about how intestinal absorption of thyroxine is impaired. They hypothesise that achlorhydria (a characteristic of atrophic gastritis and H pylori infection) may alter the ionisation status of thyroxine when it is administered as a sodium salt and thus alter the efficiency of intestinal absorption of the hormone.