Compounded Pergolide Comparisons (AAEP 2010)

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.

Stanley observed that many products fell far below labeled potency upon delivery to the test lab. Liquid preparations were unstable and potency decreased rapidly regardless of storage conditions, especially considering they were to be used within 30 days of manufacture. Powdered formulations (either in bulk form or in capsules) were less susceptible to degradation but potency levels among capsules within a single prescription bottle were erratic. Capsulated products degraded more slowly than suspension, but potency variability among capsules made it difficult to assess and interpret these products. Stanley explained that density of the pergolide chemical is 15 times greater than the lactose that is mixed with it, and inadequate mixing, in this case, distributed pergolide unevenly throughout the mix. Subsequently, some capsules were filled with too much active pergolide, while others contained too little.

The consequences of an excess or an insufficient dose of pergolide are significant in terms of toxicity or efficacy. Stanley urged all practitioners to be critical when selecting a compounding pharmacy to prepare a pergolide product for their patients.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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