Comparison of IV and IM Formulations of Synthetic ACTH for ACTH Stimulation Tests in Healthy Dogs

Background: Two commercially available forms of synthetic ACTH are used to diagnose and monitor hyper-and hypoadrenocorticism in dogs. Objective: To compare the biologic activity of the liquid and lyophilized forms of cosyntropin. Animals: Eighteen privately owned healthy dogs were included. Methods: Dogs were assigned to one of 2 groups of 9 dogs each. Group 1 dogs were tested with the lyophilized product first and the liquid solution 30-60 days later. The Group 2 dogs were tested with the liquid solution first and the lyophilized drug 30-60 days later. For the ACTH stimulation tests, serum samples were collected before and 1 hour after IM administration of 0.25 mg reconstituted lyophilized product or 1 hour after IV administration of 0.25 mg of liquid solution. Cortisol concentrations of all serum samples were measured by use of a commercial cortisol radioimmunoassay. Results: Serum cortisol concentrations before and after ACTH stimulation did not differ significantly between groups (P =.57). In addition, no individual dog had as much as a 20% difference in serum cortisol concentrations after administration of either ACTH formulation. Conclusions and Clinical Importance: Given the lack of significant differences of the ACTH stimulation test results, the lyophilized and liquid solution products can be used interchangeably.