Differences in thyroid function tests after administration of a single supraphysiological dose of ACTH or a high dose of a synthetic steroid.

Objective: Although the suppressive action of synthetic steroids on the hypothalamus-pituitary-thyroid (HPT) axis is established, little is known regarding the effect of the administration of synthetic adrenocorticotropic hormone (ACTH).

Design: In the context of a randomized, open label, comparative study assessing the efficacy and safety of ACTH and betamethasone in the treatment of hospitalized patients with acute gout, we compared the effects of these agents on thyroid function tests.

Methods: Serum TSH, total T4 and T3 and cortisol were measured before and at 24 and 48 h after a single intramuscular dose of synthetic ACTH (1 mg) or betamethasone (6 mg), in 38 hospitalized patients with acute gout and normal thyroid function.

Results: The final analysis included 32 patients, due to missing data. The ACTH and betamethasone groups did not differ regarding the mean age, gender, severity of gout attack, and baseline thyroid parameters. In the ACTH group TSH and T4 were significantly decreased at 24 and at 48 h compared to baseline, while T3 was decreased at 24 but not at 48 h. In the betamethasone group T3 remained stable; TSH and T4 decreased significantly from baseline levels at 24 h; at 48 h, TSH had returned to and T4 showed a partial rebound towards pre-treatment values.

Conclusions: A single IM administration of 1 mg of synthetic ACTH has more profound and prolonged effects on the HPT axis, lasting for at least 48 h, compared to a single IM dose of 6 mg betamethasone.