What Do We Really Know About Pergolide for Equine Cushing’s?

Pituitary pars intermedia dysfunction, known as PPID or equine Cushing’s disease, continues to plague older horses. Thought of as the most common endocrine or hormonal disease affecting elder horses, PPID occurs in about 20% of horses over the age of 15. Fortunately, an FDA-approved treatment for PPID exists, and it appears relatively effective: pergolide mesylate.

When the disease is uncontrolled and left untreated, excessive release of various proteins and mediators occurs. In turn, these potent mediators, which are released from damaged neurons in the hypothalamus, affect other regions of the brain that also secrete a surplus of hormones and mediators, essentially wreaking havoc on an aged horse’s body.

Clinical signs of PPID include lethargy, decreased athleticism or poor performance, muscle atrophy along the back, delayed shedding or excessive hair growth, regional accumulation of abnormal fat pockets, and laminitis.

Once equine PPID is diagnosed, pergolide can be administered at a rate of 2 μg/kg body weight daily. This medication functions by blocking dopamine receptors located in the hypothalamus to decrease the excessive production of hormones and other mediators.

Despite its FDA status, much remains unknown about the inner workings of pergolide (i.e., the pharmacokinetics and pharmacodynamics). In a study*, pergolide was administered at 4 μg/kg body weight daily to horses diagnosed with PPID using the thyrotropin-releasing hormone stimulation test. Pergolide levels were subsequently measured in the treated horses’ blood. Key findings included:

• Pergolide takes effect quickly, suppressing pars intermedia activity within a few hours of oral administration;
• Pergolide does not accumulate in the horse’s body, and steady levels of pergolide are realized within three days of starting treatment;
• Pergolide is cleared from the system quickly, with a half-life less than 12 hours; and
• Twice daily administration of pergolide may be more beneficial for horses with PPID (i.e., divide the total dose between morning and evening doses).

Hoof, skin, and coat health often suffer in horses with PPID. Consider offering Bio-Bloom PS (Bio-Bloom HF in Australia) to horses—even those receiving daily pergolide—to help support the health of these important structures. Bio-Bloom PS contains methionine, zinc, iodine, and biotin and is top-dressed on your horse’s feed.

Certain governing organizations consider pergolide a controlled medication, so horse owners should seek veterinary advice before use in competition horses.

*Rendle, D.I., G. Doran, J. Ireland, et al. 2019. Pharmacokinetics and pharmacodynamics of pergolide mesylate after oral administration in horses with pituitary pars intermedia dysfunction. Domestic Animal Endocrinology. 68:135-141.