Researchers have recently cautioned horse owners currently treating horses diagnosed with pituitary pars intermedia dysfunction (PPID, or equine Cushing’s syndrome) that the compounded form of the drug pergolide mesylate can become unstable and potentially ineffective.

“Since the United States Food and Drug Administration (FDA) recommended the withdrawal of human pergolide products from the market in March 2007, only compounded formulations have been available for treating horses with PPID,” explained Jennifer Davis, DVM, PhD, Dipl. ACVIM, ACVCP from the College of Veterinary Medicine at North Carolina State University.

Compounded drugs are defined as those drugs that have been manipulated in any way so that the formulation produced is different than that stated on the drug label. Compounded drugs have not been evaluated by the FDA for safety, efficacy, stability, potency, and consistency of manufacturing.

Aqueous (liquid) pergolide mesylate (1 mg/ml) was prepared and stored at -20, 8, 25, and 37° C, either protected or unprotected from light. Samples were then tested on days 0, 1, 7, 14, 21, and 35 to determine the stability of pergolide when stored under these conditions.

“Storage conditions had a major impact on the stability of pergolide mesylate as determined by a decrease in concentration of pergolide and a change in color of the compounded drug,” Davis said.

Specifically, Davis and colleagues noted that samples stored at 25° C either protected from or exposed to light underwent excessive degradation by days 35 and 14, respectively. At 35° C, samples protected from light had excessive degradation by day 21.

Based on these results, Davis and colleagues advise owners to:

• Store compounded pergolide mesylate products in a dark container, protected from light;
  
• Refrigerate products to help minimize excessive degeneration;
  
• Dispose of products within 30 days from date of compounding;
  
• Evaluate the color of the product prior to each use and discard any pergolide product that has undergone any change in color, and;
  
• Request that your pergolide is compounded by pharmacists that use only the officially recognized formula (by the United States Pharmacopeial Convention).

The study, “Effects of compounding and storage conditions on stability of pergolide mesylate,” was published in the February 2009 edition of the Journal of the American Veterinary Medical Association