The corticotrophic activity of tetracosactide in the adrenal ascorbic acid depletion test

Abstract

Abstract Using the subcutaneous adrenal ascorbic acid depletion test in hypophysectomized rats it was found that tetracosactide (synthetic 1–24 corticotrophin) could not be assayed against the International Working Standard (IWS) for natural corticotrophin because of a difference in the slopes of the dose-response curves of the preparations. Valid potency estimates were obtained when tetracosactide was assayed against a standard preparation closely similar to the 2nd International Standard for natural corticotrophin. By comparing this standard with the IWS, the best estimate of the potency of tetracosactide in terms of the IWS was 99 (92–106) units/mg. Five different batches of tetracosactide have yielded identical biological potencies. Since tetracosactide can be adequately standardized by physical and chemical-analytical criteria, labelling and dosage on a mg base instead of in units is recommended.