Pergolide Mesylate

Ergot derivative dopamine receptor agonist Prolactin inhibitor; Dopaminergic agent

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Horse PO Initial: 0.002 mg/kg (1 mg per 500 kg horse) once daily; increase by 0.5-1 mg every 2-4 weeks based on clinical response and ACTH levels. Maintenance: 1-4 mg per horse once daily (range 0.002-0.01 mg/kg). Once daily Duration: Lifelong therapy; adjust dose based on seasonal ACTH levels (higher in autumn).
Notes: Administer with a small amount of feed to reduce GI upset. Monitor ACTH levels and clinical signs every 4-6 weeks initially, then every 6-12 months.
Dog PO Initial: 0.025 mg/kg once daily; may increase to 0.05 mg/kg after 2 weeks if needed. Maximum dose: 0.1 mg/kg once daily. Once daily Duration: Lifelong; adjust based on clinical response and cortisol levels.
Notes: Use only if trilostane is ineffective or not tolerated. Monitor electrolytes and cortisol levels periodically.
Cat PO Not established; anecdotal doses of 0.025-0.05 mg/kg once daily have been used, but safety and efficacy are unproven. Once daily Duration: Variable; not recommended without specialist guidance.
Notes: Use with caution; monitor for anorexia and vomiting.

Clinical Indications & Species Uses

General Indications
  • Dopamine agonist for conditions responsive to dopamine receptor stimulation, such as hyperprolactinemia and certain endocrine disorders.
Dog (Canine)
  • Treatment of pituitary-dependent hyperadrenocorticism (PDH) (Cushing's disease) – though not first-line, may be used when trilostane is not tolerated or as an alternative.
Horse (Equine)
  • Treatment of pituitary pars intermedia dysfunction (PPID) (equine Cushing's disease).

Pharmacology & Mechanism of Action

Drug Class: Ergot derivative dopamine receptor agonist | Pharmacological Group: Prolactin inhibitor; Dopaminergic agent

Mechanism of Action: Pergolide is a potent, long-acting dopamine D1 and D2 receptor agonist. In the pituitary gland, activation of D2 receptors on lactotroph cells inhibits adenylate cyclase activity, reducing cyclic AMP levels and thereby suppressing prolactin synthesis and secretion. In the pars intermedia of the pituitary, it inhibits the secretion of pro-opiomelanocortin (POMC)-derived peptides such as adrenocorticotropic hormone (ACTH), α-melanocyte-stimulating hormone (α-MSH), and β-endorphin, which are elevated in equine pituitary pars intermedia dysfunction (PPID). This action helps restore normal hormonal balance and reduces clinical signs associated with PPID.

Pharmacodynamics: Pergolide exhibits high affinity for dopamine receptors, with a longer duration of action compared to bromocriptine. It suppresses prolactin secretion in a dose-dependent manner. In horses with PPID, pergolide reduces plasma ACTH and α-MSH concentrations, improves clinical signs such as hirsutism, laminitis, muscle wasting, and lethargy. It also has some vasoconstrictive and emetic effects due to its ergot alkaloid structure. In dogs, it is used to treat pituitary-dependent hyperadrenocorticism (PDH) by reducing ACTH secretion from the pituitary, though its efficacy is variable and it is less commonly used than trilostane.

⚡ Pharmacokinetics Summary

Absorption: Pergolide is well absorbed after oral administration in horses and dogs. Peak plasma concentrations occur within 1-3 hours. Food may affect absorption; administration with a small amount of feed may reduce gastrointestinal upset.
Distribution: Pergolide is widely distributed in tissues. It crosses the blood-brain barrier and placenta. It is extensively bound to plasma proteins (approximately 90%).
Metabolism: Pergolide undergoes extensive hepatic metabolism, primarily via oxidation and conjugation. The major metabolites are sulfoxides and glucuronides, which are less active than the parent compound.
Excretion: Pergolide and its metabolites are excreted primarily in the urine (about 70-80%) and feces (about 20-30%). In horses, the elimination half-life is approximately 2-6 hours, but the pharmacodynamic effect lasts much longer due to receptor binding.
Half-Life: Horses: 2-6 hours; Dogs: approximately 1-3 hours; Humans: 27 hours (for reference).
Bioavailability: Oral bioavailability is approximately 20-30% in horses due to first-pass metabolism; in dogs, it is about 20%.
Protein Binding: Approximately 90% bound to plasma proteins.

Available Formulations & Strengths

Oral Tablet 0.5 mg, 1 mg (PO)
Oral Capsule 0.5 mg, 1 mg (compounded) (PO)
Oral Solution (compounded) Various concentrations (e.g., 1 mg/mL) (PO)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to pergolide or other ergot derivatives.
  • Concurrent use with other dopamine antagonists (e.g., metoclopramide, phenothiazines) as they may reduce efficacy.
  • Severe hepatic or renal impairment (use with caution).
  • Pregnancy or lactation (safety not established; may affect prolactin secretion).
Warnings & Clinical Precautions:
  • Use with caution in animals with cardiovascular disease, as pergolide may cause hypotension or vasoconstriction.
  • May cause gastrointestinal upset; administer with food.
  • In horses, monitor for signs of colic, diarrhea, or anorexia; adjust dose if these occur.
  • In dogs, monitor for vomiting, diarrhea, lethargy, and electrolyte imbalances.
  • Do not use in animals with a history of psychotic disorders (rare in animals).
  • Use with caution in animals with renal or hepatic insufficiency.
  • Avoid in animals with a history of cardiac arrhythmias.

Adverse Effects & Reactions

Common:

  • Anorexia
  • Vomiting
  • Diarrhea
  • Lethargy
  • Depression
  • Weight loss

Serious / Severe:

  • Hypotension
  • Cardiac arrhythmias
  • Seizures
  • Severe gastrointestinal ulceration
  • Hepatotoxicity (rare)

Rare:

  • Fibrotic reactions (e.g., cardiac valve fibrosis) with long-term use
  • Dyskinesias
  • Hallucinations (in humans; rare in animals)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Metoclopramide Dopamine antagonist; may reduce the efficacy of pergolide. Moderate
Phenothiazines (e.g., acepromazine, chlorpromazine) Dopamine antagonists; may reduce the efficacy of pergolide. Moderate
Butyrophenones (e.g., haloperidol) Dopamine antagonists; may reduce the efficacy of pergolide. Moderate
Antihypertensive agents Additive hypotensive effects. Moderate
CYP3A4 inhibitors (e.g., ketoconazole, erythromycin) May increase pergolide plasma concentrations; monitor for adverse effects. Moderate
CYP3A4 inducers (e.g., rifampin, phenobarbital) May decrease pergolide plasma concentrations; monitor for reduced efficacy. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Severe vomiting
  • Diarrhea
  • Hypotension
  • Tachycardia or bradycardia
  • Agitation
  • Tremors
  • Seizures
  • Respiratory depression

Emergency Treatment Protocol: Induce emesis if recent ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Provide symptomatic and supportive care: IV fluids for hypotension, antiemetics (e.g., maropitant) for vomiting, anticonvulsants (e.g., diazepam) for seizures, and cardiac monitoring. There is no specific antidote; dopamine antagonists (e.g., metoclopramide) may be used cautiously to reverse severe effects, but they may also reduce therapeutic efficacy.

Food Animal Withdrawal Times

Not approved for food animals; no withdrawal times established. Do not use in animals intended for human consumption.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F); excursions permitted between 15-30°C (59-86°F).

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep in a tightly closed container. Compounded formulations may have different storage requirements; follow label instructions.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: FDA-approved for use in horses (Prascend, 0.5 mg and 1 mg tablets). Not FDA-approved for dogs or other species; use in dogs is extra-label.

Extra-Label (Off-Label) Use: In the US, pergolide is FDA-approved for use in horses (Prascend) and is a prescription drug. Extra-label use in other species is permitted under AMDUCA (Animal Medicinal Drug Use Clarification Act) provided there is a valid veterinarian-client-patient relationship, and no approved drug is available. For food animals, extra-label use is prohibited if it results in violative residues; no withdrawal times are established.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Pergolide is the drug of choice for equine PPID (Cushing's disease). Treatment is lifelong, and dosing must be individualized based on clinical response and ACTH levels. In horses, the dose is often adjusted seasonally, with higher doses needed in the autumn when ACTH levels naturally rise. In dogs, pergolide is a second-line treatment for PDH, as trilostane is generally preferred; however, pergolide may be useful in dogs that do not tolerate trilostane. Adverse effects are primarily gastrointestinal, and starting with a low dose and titrating slowly can minimize them. Monitoring includes regular physical examinations, serum biochemistry, and hormone assays (ACTH, cortisol). In horses, monitor for laminitis and other PPID complications. Due to the risk of fibrotic reactions with long-term use, periodic cardiac evaluation may be considered in animals on prolonged therapy, although this is rare in veterinary medicine. Always use with caution in animals with cardiovascular disease. Compounded formulations should be used with caution due to potential stability and potency issues. Client education is essential to ensure compliance and understanding of the chronic nature of therapy.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)