Pergolide has been the mainstay treatment of pituitary pars intermedia dysfunction (PPID), also known as equine Cushing’s disease, for several decades. Due to the class of drug that pergolide represents, it is a prohibited substance under Fédération Equestre Internationale and United States Equestrian Federation (USEF) rules.
Currently, under USEF GR411, “Conditions For Therapeutic Administrations of Prohibited Substances,” pergolide can be administered, but requires a 24-hour withdrawal from treatment prior to competition, which can represents a hardship to competitor and horse. However, effective Dec. 1, horses that are granted a therapeutic use exemption (TUE) for pergolide can remain on the drug with no withdrawal of drug prior to competition and no need to file a medication report form (MRF) each time they compete.
The USEF recognizes the benefit of this medication in the treatment of PPID-affected horses to normalize the endocrine feedback mechanisms disrupted by this disease. Modeled after TUEs for human athletes that are sanctioned by the World Anti-Doping Agency, the USEF TUE process is intended to sanction the daily administration of pergolide to PPID-affected horses.
To obtain a TUE for pergolide, owners/trainers should submit the required medical records and results of specific diagnostic testing for PPID, obtained from a treating veterinarian, by using the updated electronic MRF and clicking the new pergolide check box. A three-veterinarian review panel will decide whether the submitted documents support the diagnosis of PPID.
Upon approval, the horse will be granted a TUE for up to three years. At the conclusion of this time, a request can be made to extend the TUE. The review process could take up to 30 days to complete once all relevant information has been submitted. It is anticipated that the timeline will become shorter, but to manage expectations in a new process, this timing will be communicated. Once granted, a TUE would be effective for three years, after which the owner/trainer can request an extension.
The most common disease in geriatric horses, veterinarians have begun to recognize PPID in some younger horses, as well. Affected equids show a variety of clinical signs, including excessive hair growth with reduced to no seasonal shedding, frequent urination and drinking, immunosuppression, muscle wasting, and laminitis.
The condition results from degeneration of dopaminergic nerve cells in the brain’s hypothalamus, which causes an increased production of the hormone ACTH and other peptides. Increased ACTH concentrations stimulate the adrenal glands to increase release of corticosteroids into an affected horse’s blood stream.
Epidemiologic studies have shown that one in five horses over 15 years of age has PPID, and one in eight of these horses could also develop laminitis. In fact, horses with PPID are four times more likely to founder than horses without PPID. Untreated PPID poses a significant threat to the welfare of the horse population in general and could compromise or end the competitive career of equine athletes.
At this time, there are no plans to add additional medications to the TUE process, but that could change in the future.