Endocrine Abstracts

BACKGROUND Recent evidence has suggested that minor degrees of thyroid dysfunction are associated with adverse outcomes and this argues for tight control of thyroid hormone replacement. Thyroxine (T4) tablets are available in 25, 50 and 100 microgram strengths in the UK but some patients require doses which cannot be obtained with these strengths. We have examined data from a thyroid register to determine the proportion of patients whose mean daily T4 dose cannot be achieved with the currently available tablet strengths.

METHODS A sample of 300 patients on the North Trent thyroid register who had an abnormal TSH level and whose T4 dose was altered was examined retrospectively. For each patient the initial and final TSH level and T4 dose were recorded.

RESULTS 151 patients had a dose adjustment because of TSH values which were either undetectable or above 10 milli-international units per litre, the remainder had less extreme TSH values. In 171 patients TSH level normalised whilst on a standard T4 dose but 46 patients required a split T4 dose i.e. differing doses on alternate days; the remainder were still undergoing dose titration and have not been analysed. Of the patients requiring split doses, 33 needed a mean daily dose of either 87.5 or 112.5 micrograms.

CONCLUSION A small minority of patients with primary hypothyroidism require T4 dosages which cannot be achieved with a constant daily dose using the available tablet strengths. Currently this necessitates prescription of differing T4 doses on alternate days but this is unpopular and likely to impair adherence to treatment. Provision of a new tablet strength of 37.5 microgram would allow dose adjustment in 12.5 microgram increments, rather than the current 25 microgram increments, and would allow virtually all patients to achieve optimum TSH concentrations whilst on a constant daily T4 dose.