Pergolide (pergolide mesylate) is a dopamine agonist that is used to control the symptoms associated with equine pituitary pars intermedia dysfunction (PPID).¹ It is currently the only medication licensed for the treatment of PPID in horses. 

Pituitary pars intermedia dysfunction, also known as Cushing’s Disease, affects hormone production pathways in the brain from the hypothalamus and pituitary glands. The release of hormones from the pituitary gland is normally controlled by the hypothalamus through the neurotransmitter dopamine. In the presence of PPID, the degeneration of neurons that produce dopamine results in an inability to control the hormones produced by the middle lobe of the pituitary gland (pars intermedia). High levels of these hormones affect processes throughout the body. PPID is age-related, typically occurring in horses older than 15 years of age, although horses as young as 7 years of age have reportedly been diagnosed with PPID.²

Pituitary pars intermedia dysfunction and equine metabolic syndrome (EMS; a more recently described syndrome that shares some characteristics with PPID) are often encountered in aging horses and may present with several recognizable signs, including laminitis.³ Diagnoses and treatments for PPID 6and EMS differ, so it is important to have an experienced equine veterinarian diagnose horses suffering from the described symptoms.

Common signs of PPID in horses include:

• Failure to fully shed
• Long, curly coat (often along the jaw line with feathering near the fetlocks)
• Chronic infections
• Repeated occurrences of laminitis with hoof abscesses
• Excess sweating
• Polyuria/polydipsia (PU/PD)
• Lethargy
• Loss of muscle mass (in untreated horses)
• Pot-bellied appearance
• Infertility, or lack of estrus cycles
• Abnormal development of mammary glands

Approximately 30% of horses with PPID also show signs of insulin dysregulation. In these horses, blood insulin levels are high because tissues have a decreased insulin response. Insulin dysregulation is usually indicative of EMS. PPID and EMS can present at the same time in the same horse, so knowledge of a horse’s insulin status is important for assessing laminitis risk and determining dietary management.⁴

Pergolide for Horses

Pergolide serves to decrease some of the hormone production by the pituitary gland. Several studies have addressed its usefulness in PPID-affected horses and shown significant improvements in hair coat, frequency of urination and drinking, frequency of infections and laminitis bouts, and many laboratory test results.³ Pergolide is a potent agonist at dopamine receptors (D1 and D2) and is 10-1000 times more potent than bromocriptine. The literature holds that pituitary pars intermedia dysfunction (PPID) in horses is a dopaminergic degenerative disease and pergolide (or dopamine) can reduce expression of proopiomelanocortin (POMC) peptides from the pars intermedia.¹

In horses, pergolide was rapidly absorbed following oral administration with plasma concentrations reaching maximum levels within 1 hour of dosing. Maximum plasma levels ranged from 1.07-3.38 nanograms/mL. Pergolide appears to be rapidly and widely distributed.¹

Pergolide appears to be well tolerated in horses. Decreased appetite is seen during the first week of therapy in ≈10% of horses treated; temporary dose reduction is often beneficial in alleviating this effect. Colic and diarrhea have been reported to occur more rarely.^1,3

Recommended dosages for horses with PPID is oral administration with a starting dose of 2 micrograms/kg once daily. This may be adjusted to effect, not to exceed 4 micrograms/kg daily.¹ While pergolide does not cure PPID, clinical signs should show improvement within 1-3 months. Ongoing monitoring is important and retesting should be performed at least twice a year, with one assessment during the fall, to determine if there is a need for changes in medication.

The prognosis for horses with PPID varies, with some horses responding to a low level of medication and others needing a much higher level. Earlier diagnosis may result in a better quality of life, particularly if negative consequences like infections and laminitis can be avoided.⁴

Where to buy Pergolide

Pergolide is available in the U.S. through several pharmaceutical manufacturers and through veterinary custom compounding companies. PERGOLIDE 1.5MG/ML ORAL SUSPENSION by NexGen Pharmaceuticals is indicated for the treatment of pituitary pars intermedia dysfunction (PPID) in the horse.

This product carries minimal potential drug interactions, however it is advisable to consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

¹Plumb’s Veterinary Drugs.

²Durham, A. Endocrine Disease in Aged Horses. Vet Clin North Am Equine Pract. 2016 Aug; 32(2):301-15. 

³McFarlane, D. Equine pituitary pars intermedia dysfunction. Vet Clin North Am Equine Pract. 2011 Apr; 27(1):93-113.

⁴aaep.org.