Systemic effects of equine Cushing's disease, a common malady in older horses, have been controlled well in many horses with daily administration of pergolide. Until 2007 this medication was available for off-label use–the human product was available for purchase. Then, the FDA-approved product was removed from the human pharmaceutical market. The product had to be compounded in order to be available to the equine population, so quality control issues became a large concern. Scott Stanley, PhD, of the K.L. Maddy Equine Analytical Chemistry Laboratory at the University of California, Davis, discussed efficacy, potency, and stability of compounded pergolide preparations at the 2010 American Association of Equine Practitioners Convention, held Dec. 4-8 in Baltimore, Md.

In a recent study Stanley examined the potency and stability of three different compounded pergolide products–liquid suspensions, powders in bulk form, and powder-filled capsules–relative to storage duration and varied storage temperatures. In previous studies and reports, authors recommend that storage should not exceed 30 days and that pergolide products–particularly those in liquid suspension form–are best stored at 8°C (46° F).

Stanley began his discussion by addressing liquid suspensions, noting that three out of seven tested suspensions did test as having the target potency prior to storage. However, after storage, potency decreased to 30-40%, even at 8°C (46°F). After 60 days, the potency of most products stored at 25°C (77°F) with exposure to light fell below 70% of the target potency and were inconsistent from lot to lot.

Storage temperature did not appear to affect powdered or capsulated forms of pergolide. Four out of seven products (each from different compounding pharmacies) started at levels above the target potency, however active medication in each capsule varied by as much as 200%. Stanley concluded that potency testing at the compounding pharmacy that produced the compounded capsules that tested higher than 200% was lacking during preparation, and stability data (evaluations that are carried out to study the chemical and physical stability of formulations) was unavailable