Steroidal response following intravenous administration of long-term frozen tetracosactide acetate in healthy Beagles

Background The adrenocorticotropic hormone (ACTH) stimulation test is used to assess adrenal function. The effects of extended freezing of tetracosactide acetate (TCA), an ACTH analogue, on test performance, remain unexplored. Hypothesis/Objectives To determine whether TCA retains its biological activity to induce adrenal steroid production when stored in plastic syringes and frozen at −20 °C for prolonged period. Animals Eight adult experimental Beagles divided into 2 groups of 2 males and 2 females each. Methods Prospective case-crossover study. Each dog received 5 μg/kg IV of TCA on 2 occasions, 4 weeks apart (period P1–washout–period P2). Group 1 received frozen then fresh TCA; group 2 received fresh then frozen TCA. Pre- and post-administration blood samples were analyzed at both study periods for cortisol and other steroid metabolites using liquid chromatography–tandem mass spectrometry. A general linear mixed model was used with TCA (fresh vs frozen), period, sequence and timing as fixed factors, and dog as random factor. Results Frozen TCA stored for a median time of 1.8 years (IQ range 1.5-1.9) induced similar steroid metabolite responses compared with fresh TCA. Median T1 cortisol concentrations were 248 nmol/L (IQ range 231-272) with frozen TCA and 254 nmol/L (IQ range 249-262) with fresh TCA (P = .037). Median T1 17-OHP concentrations were 0.73 μg/L (IQ range 0.67-0.85) with frozen TCA 0.79 μg/L (IQ range 0.71-1.17) with fresh TCA (P = .09). Conclusions and clinical importance Long-term freezing of TCA in plastic syringes offers a cost-effective strategy and practical alternative during supply shortages.