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.