Bromocriptine

Bromocriptine is an ergot-derived dopamine agonist used for prolactin-dependent reproductive disorders, especially in dogs. Suppression of prolactin can reduce lactation and signs of pseudopregnancy, and it has been used as a partner in selected pregnancy-termination protocols. Its emetic and other adverse effects can limit tolerability.

It has also been investigated for pituitary and endocrine disorders, but usefulness differs by disease and species. Historical use in equine pituitary dysfunction does not establish it as a preferred treatment, and it has not proved effective for canine pituitary-dependent hyperadrenocorticism.

Group

Dopamine agonist and prolactin inhibitor

Mechanism of Action

Bromocriptine stimulates dopamine D2 receptors on pituitary lactotroph cells, strengthening the inhibitory dopaminergic signal that restrains prolactin secretion. Lower circulating prolactin reduces prolactin-dependent mammary activity and milk production, explaining its principal reproductive applications.

Prolactin also provides luteal support during part of canine gestation. Reducing this support can contribute to loss of progesterone maintenance and pregnancy termination, particularly when combined with a luteolytic prostaglandin. Response therefore depends on gestational stage and the hormonal dependence of the corpus luteum.

Dopaminergic actions at other central and pituitary sites account for additional pharmacologic and adverse effects, including vomiting. Activity at a dopamine receptor does not ensure effective suppression of every pituitary hormone or treatment of every pituitary tumor, which explains the uneven results in nonreproductive endocrine disorders.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Pregnancy termination	Reference only	PO		Use the staged bromocriptine–cloprostenol course described under Monitoring and Administration; this is a combination protocol.
Lactation suppression	Reference only	PO		10–100 mcg/kg every 12 hours for 10–14 days. The dosage bullet does not explicitly identify the administration route.
Pseudopregnancy	10–30 mcg/kg	PO	Every 12 h	If adverse effects occur, reduction to 7.5 mcg/kg is described.
Other endocrine conditions	20–40 mcg/kg	PO	Every 12 h	The source does not identify a specific endocrine diagnosis for this general regimen.
Lactation suppression	10–100 mcg/kg	PO	Every 12 h	Up to 14 days; Course 10–14 days; food and dose reduction may reduce vomiting.
Pseudopregnancy	10–50 mcg/kg	PO	Every 12 h	An alternative described at least twice daily; adjust to prolactin signs and tolerance.
Pregnancy termination	50–100 mcg/kg	PO, IM	Every 12 h	Up to 7 days; Start 35–45 days after the LH surge; course 4–7 days. Not uniformly effective; vomiting is common. Injectable use requires an appropriate sterile preparation.
Pregnancy termination with cloprostenol	Reference only	PO		From approximately 25 days after the LH surge: bromocriptine 30 mcg/kg orally every 24 hours plus cloprostenol 1 mcg/kg SC every 48 hours; this differs from the staged bromocriptine course already listed.

Cats

Use / stage	Dose	Route	Schedule	Instructions
Other endocrine conditions	20–40 mcg/kg	PO	Every 12 h	The source does not identify a specific endocrine diagnosis for this general regimen.
Acromegaly adjunct	Reference only	PO		An initial total dose of 0.2 mg is described, but route and repeat schedule are not assigned; insulin needs may change.

Horses

Use / stage	Dose	Route	Schedule	Instructions
Pituitary dysfunction	30–90 mcg/kg	PO, SC	Every 12 h	Limited-use historical alternative; pergolide is generally preferred.
Pituitary dysfunction	5 mg/animal	IM	Every 12 h	Requires an appropriate sterile injectable formulation; do not inject an unvalidated oral-tablet mixture.

Indications

Treatment of canine pseudopregnancy with prolactin-associated mammary or behavioral signs.
Suppression of unwanted lactation in selected bitches.
Selected canine pregnancy-termination protocols in combination with a prostaglandin.
Historical treatment of equine pituitary pars intermedia dysfunction; supporting evidence is limited.
Investigational adjunctive treatment of selected endocrine disorders, including acromegaly-related applications.

Contraindications

Pregnancy except intended termination.
Lactation when continued nursing is desired.
Hypertension; use cautiously with hepatic impairment.

Interactions

Do not combine with MAO inhibitors, including selegiline.
Cyclosporine concentrations may increase; dopamine antagonists can reduce efficacy.
Erythromycin, clarithromycin and octreotide may raise bromocriptine exposure.
Other hypotensive agents can worsen hypotension; other ergot drugs or sympathomimetics can produce serious cardiovascular interactions.
Estrogens or progestins can oppose the desired endocrine effect; metoclopramide can increase prolactin release.

Adverse effects

Vomiting, nausea and retching
Hypotension
Mammary changes
Pyometra after pregnancy termination

Preparations

Preparation	Form	Strength	Route
Bromocriptine 2.5 mg tablet	Tablet	2.5 mg / tablet	PO
Bromocriptine 5 mg capsule	Capsule	5 mg / capsule	PO

Monitoring and Administration

Confirm complete pregnancy termination and monitor uterine discharge.

For pregnancy termination, give orally 15 mcg/kg every 12 hours on day 1, 20 mcg/kg every 12 hours on days 2–3, then 30 mcg/kg every 12 hours. Treatment averages 4–5 days but may require 10 days. Combine with cloprostenol 1 mcg/kg subcutaneously every 48 hours.

A 2.5 mg tablet dissolved to a final 10 mL gives 250 mcg/mL. Refrigerate in amber glass and use within one week. Avoid exposure during handling, particularly for women who may be pregnant.