Research on Long-Term Treatment of PPID Horses

Long-term treatment (2.5 to 14+ years) of PPID in horses is beneficial, according to new research. PPID (pituitary pars intermedia dysfunction) is also known as Cushing’s disease. FDA-approved treatment of equine PPID is with Prascend (pergolide mesylate).

PPID is a slowly progressive disorder. Pergolide is recommended as a life-long daily treatment for equids with PPID. Harold Schott, Julie Strachota, Judith Marteniuk, and Kent Refsal authored this research.

(Editor’s note: Schott is a member of the My Senior Horse Editorial Advisory Group.)

The study concluded that “Long-term treatment of PPID-affected equids with pergolide produces clinical improvement in nearly all affected animals and normalization of endocrine test results in some cases. Furthermore, this extended treatment study determined that equids can respond favorably long-term to the initial pergolide dose, rather than needing a progressive increase in dose over time.”

The study was titled “Long-Term Response of Equids With Pituitary Pars Intermedia Dysfunction to Treatment With Pergolide.” It was published in the Journal of Veterinary Internal Medicine.

The purpose of the study was to characterize long-term clinical response, endocrine test results, medical problems (potential adverse effects), outcome, and owner satisfaction in a cohort of equids enrolled in an extended use study of Prascend® (pergolide tablets).

“Although the primary focus of the extended use study was to document the long-term safety of pergolide, clinical responses and endocrine test results also were evaluated after 2.5, 3, 3.5, 4.5, 5.5, 6.5, 9.5, 12.5, and 14.5 years of treatment,” noted the researchers.

Senior Horses and PPID

The researchers noted that USDA information indicated an increase in equids aged 20–29 years from 7.6% to 11.4% of the total equine population between 2005 and 2015. “Similar surveys in the United Kingdom (UK) and Australia indicated that 29% and 33% of equids were 15 years or older, respectively, with 2.2% of the UK equine population >30 years old,” they noted.

PPID is the most commonly recognized endocrinopathy of aged equids. There was a prevalence of 2.9% in a population of 70,000 equids in seven United Kingdom veterinary practices.

Hair coat changes—an easily identifiable clinical sign of PPID—have been reported in >20% of equids that are 15 years of age or older in Australia and the UK. In equids more than 30 years of age, greater than 30% have been identified with hair coat changes consistent with PPID.

There is an approved treatment for equine PPID (Prascend). In 2011, the FDA found that Prascend (from Boehringer Inghelheim) improved clinical signs and endocrine test results in a group of PPID-affected horses and ponies after 180 days of treatment. Improvements were seen in 86 of 113 animals (76%).

The Research

“The extended use study included 28 horses and two ponies and consisted of 17 geldings and 13 mares,” noted the researchers. “Estimated mean age at enrollment was 23.1 years (range 17–29 years).”

Breeds included in this study were nine Arabians or Arabian crosses, six Morgans or Morgan crosses, six Quarter Horses or Quarter Horse crosses, two Thoroughbreds, two ponies, one Tennessee Walking Horse, one Missouri Fox Trotter, one Paso Fino, one Fjord, and one mixed breed horse.

While some horses had their dosages of pergolide mesylate increased over the years based on oral dexamethasone suppression tests (ODST), about half did not require dosage incrases.

Horse Owner Survey

Twenty-five of 29 owners of test horses completed a survey. (One owner had two horses in the study.) Seventy-one percent strongly agreed and 25% agreed that treatment with Prascend improved their perception of the equid’s quality of life. Seventy percent strongly agreed and 30% agreed that Prascent prolonged their horses’ lifespan.

Improvement in clinical signs with Prascend treatment was most satisfactory for energy level (77%), hair coat (71%), and muscle mass (61%).

Overall satisfaction with treatment on a scale of 1–10 (10 best) was 10: 52%, 9: 17%, 8: 13%, 7: 9%, 5: 9%, and 7: 9%. The survey showed that 87% of owners either agreed or strongly agreed that they would provide lifelong treatment if they had another equid with PPID.

However, medication cost would be a factor. Twenty-six percent of owners were willing to pay $500 annually for medication, and 57% of owners were willing to pay $1,000 annually. Only 17% of owners would be willing to pay ≥$1,500 annually.

All owners responding to the survey thought that treatment with Prascend prolonged their equid’s lifespan and improved quality of life. However, researchers noted that, “Our study did not produce data to support this claim because a cohort of untreated PPID-affected equids was not followed over the same time period.”

Final Words

The results show that long-term (> 5 years) treatment of PPID-affected equids with pergolide mesylate produced clinical improvement in nearly all surviving equids. There was normalization of endocrine test results in > 60% of cases. Owner satisfaction with treatment was high.

“To our knowledge, our study is the first long-term treatment study to provide evidence that equids may continue to respond favorably to the initial pergolide dose, rather than requiring an increase in dose over time,” noted the authors.

The research stated that changes in appetite varied in severity and duration in the extended use study and were unrelated to starting or changing the dose of Prascend. It was uncertain whether decreases in appetite were associated with the drug or simply a problem that can wax and wane in aging equids

“Long-term treatment with pergolide mesylate improved the quality of life of PPID-affected equids, leading to high owner satisfaction,” noted the authors. “Our findings complement published recommendations for veterinarians advising owners about the medical treatment of PPID-affected equids. However, veterinarians should be cautious in suggesting that pergolide treatment might prolong life, because the cause of death or decision for euthanasia was unrelated to PPID in most equids lost during this study.”