Metergoline
**Metergoline** is an **ergot-derivative** medication primarily utilized in veterinary medicine to manage **pseudopregnancy (false pregnancy)** in dogs. Key clinical points: - Acts as a **prolactin inhibitor** to stop unwanted lactation and behavioral changes associated with false pregnancy. - Has been investigated as an abortifacient at high doses (0.4-0.6 mg/kg) during the last 3 weeks of gestation. - Not commercially available in the USA, but widely used as a veterinary product in several European and South American countries. - In human medicine, it is used for hyperprolactinemia, prolactinomas, and migraine prophylaxis.
Mechanism: Metergoline reduces prolactin secretion primarily through its **serotonin receptor antagonism**. Mechanistic pathway: - **Serotonin (5-HT) antagonism** → Inhibition of prolactin release from the anterior pituitary. - Unlike other prolactin inhibitors (e.g., cabergoline, bromocriptine), it possesses strong central and peripheral anti-serotonin effects. - Exhibits weak direct **dopamine-2 (D2) agonist** effects and acts as an antagonist at **dopamine-1 (D1) receptors**.
Dosing by species
- Treatment of pseudopregnancy or to halt post-partum lactation · 0.125 mg/kg PO twice a day · PO · q12h · 4-8 days
- Treatment of pseudopregnancy · 0.5 mg/kg (500 micrograms/kg) PO twice a day · PO · q12h · 4-5 days · Occasional failures can be dealt with by repeating the treatment protocol and extending it to 8 to 10 days, or by using joint protocols of cabergoline plus metergoline or cabergoline plus bromocriptine.
- Treatment of pseudopregnancy · 0.1 mg/kg, PO twice a day · PO · q12h · 8 to 10 days
- Treatment of pseudopregnancy · 0.1 mg/kg q12h PO with food · PO · q12h · 10 days · Side effects were limited to hyperexcitation and nausea, did not lead to termination of therapy, and gradually dissipated during the second week.
- To induce estrus · 0.1 mg/kg PO twice a day · PO · q12h · From 100 days after ovulation until the following proestrus · Results have been variable depending on dosage. Can significantly shorten the interoestrous interval.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Pregnancy (unless abortion is desired)
- Nursing mothers
- Hypersensitivity to ergot derivatives
Adverse effects
- Anxiety
- Aggressiveness
- Depression
- Hyperexcitation
- Whining
- Escaping behavior
- Anorexia
- Vomiting
- Nausea
Drug interactions
- Bromocriptine · May cause additive effects if used with metergoline
- Cabergoline · May cause additive effects if used with metergoline
- Cyproheptadine · May cause additive effects if used with metergoline
- Metoclopramide · Use with metergoline may reduce the efficacy of both drugs and should be avoided
- SSRIs (e.g., fluoxetine, paroxetine, sertraline) · Potentially could reduce the efficacy of each drug
Monitoring
- Clinical efficacy (resolution of pseudopregnancy signs)
- Adverse behavioral or GI effects
- Liver function tests (if used long-term)
Overdose
Little information is available regarding acute toxicity. **Vomiting** is the most likely clinical sign expected in an overdose situation. Treatment should be supportive and symptomatic.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.