Pituitary pars intermedia dysfunction (PPID), often called equine Cushing's disease, has been treated with the drug pergolide for years. The main reason pergolide was initially the treatment of choice was largely based on the drug's effectiveness in treating people with Parkinson's disease, a human endocrine disorder, according to Ronette Gehring, BVSc, MMedVet (Pharm), MRCVS, Dipl. ACVCP, of Kansas State University, who recently published a study reinforcing the usefulness of oral pergolide in horses.
There has been little research done on the drug in horses, noted Gehring, who is an assistant professor in the department of clinical sciences, although a group of researchers from Michigan State University completed a study, lasting from 1997 to 1999, on the efficacy of pergolide in horses, revealing that pergolide was more effective in controlling PPID than another treatment option available to horse owners.
But according to Gehring there was little known about how well horses actually absorb pergolide.
"We didn't even know if horses absorbed the pergolide following oral administration," Gehring said. Gehring and a team of researchers sought to correct this lack of knowledge by testing the drug to see how well a horse's system absorbs and metabolizes it. The study results revealed that oral doses of pergolide are absorbed within 30 minutes of administration, and that the drug's half life (or the time required for the drugs' blood concentration to decrease by 50%) was 27 hours.
"Pergolide is administered daily, and costs can add up with this drug," Gehring said. "Owners should feel more comfortable knowing that pergolide is well-absorbed following oral administration."
Gehring's study results might also help veterinarians adjust pergolide doses in horses. Gehring said that pergolide's pharmacokinetics (the factors affecting the concentration of the drug at the site of action, which in turn affects the onset, duration and magnitude of effect) are similar in horses and humans, so dosing regimens based on studies in humans are likely to be clinically effective in horses as well.
PPID is a common condition in older horses that results in clinical signs that can include a long hair coat (hirsutism), delayed shedding of the winter hair coat, loss of muscle mass, increased drinking and urination, a pot-bellied appearance, and an increased susceptibility to infections. If left untreated, Cushing's horses generally experience chronic bouts of disease, a decline in health and comfort, and reduced quality of life.
Gehring and her colleagues plan to continue studying this drug to determine the optimum equine dosing schedule.
The study, "Single-dose oral pharmacokinetics of pergolide mesylate in healthy adult mares," appeared in the spring issue of Veterinary Therapeutics. The abstract can be viewed online at PubMed.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.