Pergolide Alert!

Pergolide for Veterinary Use

Basic Pergolide Information

Pergolide is a drug that was used in humans for the treatment of Parkinson’s disease. As of 2007, the FDA has withdrawn pergolide from the human market due to cardiac complications. Pergolide remains the drug of choice for the treatment of pituitary pars intermedia dysfunction (PPID) also known as Equine Cushing’s Syndrome (ECS) in the horse. PPID is one of the most common diseases of older horses and ponies. Compounded pergolide for veterinary use remains available because the Center for Veterinary Medicine division of the FDA recognized how important this drug is for the health and welfare of many older horses.

Pergolide for Horses

Our knowledge of endocrine diseases of the older horse has exploded in the last 10 or 15 years. PPID is a neurodegenerative disease originating in the hypothalamus which affects the pars intermedia portion of the pituitary gland. Animals with PPID have as much as an eight fold decrease in the neurotransmitter dopamine when compared to control animals. Recent research suggests that the dopamine producing neurons in the pars intermedia decrease or almost vanish in these horses. Pergolide is a dopamine agonist. Its mechanism of action is through the binding of drug receptors in the brain that control dopamine production. Although the use of pergolide in the horse is extra-label, it is an established therapy and has improved or saved the lives of thousands of horses for over 20 years.

Clinical signs of PPID include abnormally long hair coat (hirsutism) and failure to properly shed, abnormal fat distribution, laminitis (greater than 50% of animals), increased water consumption and increased urination (greater than 30% of animals), muscle wasting, compromised immune function, and abnormal cycling in mares. Ponies and some breeds of horses including Morgans appear to be at increased risk for the development of PPID. PPID is a medical problem that is managed, not cured. Animals that are being treated are usually on medication for the rest of their lives.

There has been recent discussion of a similar endocrine problem in horses referred to as Equine Metabolic Syndrome. Although these animals present with insulin resistance and some of the same clinical signs as horses with PPID (particularly obesity, laminitis, enlarged fat pads and a cresty neck), this is probably a separate endocrine disease and is not as likely to respond to treatment with pergolide.

PPID is frequently diagnosed by clinical signs alone, particularly in cases where hirsutism is present. Possible diagnostic endocrine tests include diurnal cortisol rhythm, ACTH levels, dexamethasone suppression test, thyrotropin releasing hormone (TRH) stimulation test, and insulin levels. At this time there is no agreed upon “gold standard” test and different cases will need the clinical judgment of the attending veterinarian. For those seeking more information, there is an excellent review of PPID and other endocrine problems of the horse in the 2006 AAEP Proceedings.

Side Effects and Precautions for Pergolide use

• The most common side effect is a decrease in appetite at the beginning of treatment. This may be managed by stopping treatment for a few days, and then beginning again at one half the dose; gradually increasing to the full dose.
• It is important to identify and use the lowest possible dose of pergolide. There is some thought that this condition may over time become resistant to medication.
• High doses of pergolide have been tested in laboratory animals without causing detectable harm to the fetus. This work has not been done in horses. It is not known if pergolide is excreted in milk but this type of drug may interfere with lactation. Pergolide has been used in pregnant mares but no formal studies have been performed. No information was found on pergolide use in breeding stallions

Drug Interactions and Overdose with Pergolide

• Phenothiazine tranquilizers such as acepromazine may interfere with the action of pergolide.
• Overdose in humans causes gastrointestinal upset and hallucinations. Some of the compounded forms of pergolide are available as a “treat.” It is important to be aware that these are medications and should only be given in the prescribed dose.

About the Author

Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982. She began to develop her interest in client education and medical writing 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse. Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA. You can purchase books by Dr. Forney at www.exclusivelyequine.com