# Metformin: veterinary dose and monograph

> Metformin is a veterinary drug. A biguanide oral antihyperglycaemic that lowers blood glucose mainly by reducing hepatic gluconeogenesis and improving INSULIN SENSITIVITY (it does not stimulate insulin secretion, so it does not cause hypoglycaemia on its own). Indications include feline type-2-like diabetes / insulin resistance (limited, generally unsuccessful — insulin preferred); equine insulin dysregulation / equine metabolic syndrome (adjunct, investigational); hyperinsulinaemia-associated conditions where improving insulin sensitivity is the goal (experimental). This monograph lists 2 reference doses for cats and horses, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/metformin · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Veterinary drug
- **Also known as:** Glycomet, Glucophage, Metformin HCl
- **Species with doses:** Cats and Horses
- **Routes:** PO
- **Last reviewed:** 1 October 2026

## Indications

- Feline type-2-like diabetes / insulin resistance (limited, generally unsuccessful — insulin preferred)
- Equine insulin dysregulation / equine metabolic syndrome (adjunct, investigational)
- Hyperinsulinaemia-associated conditions where improving insulin sensitivity is the goal (experimental)

## Metformin dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Cats

*Metformin doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Type-2 diabetes (residual insulin; limited efficacy) | 25–50 mg per cat PO q12h (≈2–10 mg/kg) | PO | q12h | — |

- Type-2 diabetes (residual insulin; limited efficacy): Papich 5e: 25 or 50 mg per cat q12h (5–10 mg/kg); efficacy limited. Plumb’s p.793: 50 mg per cat q12h, only in cats with detectable insulin (Nelson); 2 mg/kg q12h for early NIDDM (Melendez); Greco considers it toxic and ineffective in cats. Insulin remains standard; monitor renal function.

### Horses

*Metformin doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Insulin dysregulation / EMS — Papich 5e | Not recommended — Papich 5e: oral bioavailability in horses is only 4–7% with high clearance | — | — | — |
| Equine metabolic syndrome — adjunct (Plumb’s 10e; controversial) | 30 mg/kg | PO | q8–12h, 30–60 min before feeding | — |

- Insulin dysregulation / EMS — Papich 5e: Papich 5e: because of high clearance and poor bioavailability (4–7%) in horses, use is not recommended; consistently effective horse doses are not established. REFERENCE CONFLICT: Plumb’s 10e p.841 gives an adjunctive dose (next row). Manage insulin dysregulation with diet and exercise first.
- Equine metabolic syndrome — adjunct (Plumb’s 10e; controversial): Plumb’s 10e p.841 (extra-label): use is controversial and evidence for efficacy conflicts. Reserve for horses and ponies with markedly increased oral sugar test insulin concentrations even after loss of body fat and dietary management; current recommendation 30 mg/kg PO every 8 to 12 hours, preferably 30–60 minutes before feeding. REFERENCE CONFLICT: Papich 5e does not recommend use in horses (row above).

## Contraindications

Renal impairment (reduced clearance → lactic-acidosis risk), hepatic disease, hypoxaemia/poor tissue perfusion/dehydration (lactic-acidosis risk), and diabetic ketoacidosis (use insulin). Concurrent contrast agents/anaesthesia in compromised patients. Known hypersensitivity. Insulin-dependent diabetes (ineffective alone).

## Species-specific warnings

> **Caution:** Cats: Frequently ineffective and poorly tolerated (anorexia/weight loss) in diabetic cats — insulin is the standard of care; reserve metformin for select insulin-resistant cases and monitor renal function.

## Adverse effects

- GI upset (anorexia, vomiting, weight loss) — common in cats, often limiting
- Lactic acidosis (rare but serious, esp. with renal/hepatic impairment or hypoperfusion)
- Does not cause hypoglycaemia alone (no insulin secretion)

## Drug interactions

- Insulin / other hypoglycaemics: additive glucose lowering
- Iodinated contrast / nephrotoxins: increased lactic-acidosis risk (renal effect)
- Cimetidine: raises metformin levels (reduced renal clearance)
- Drugs causing hyperglycaemia (corticosteroids): antagonise control

## Pregnancy and lactation

Limited veterinary data; generally not used in pregnancy in animals.

## Monitoring

- Blood glucose / clinical response (efficacy is often poor in animals)
- Renal function (lactic-acidosis risk) and hydration
- GI tolerance (anorexia/weight loss — common reason to stop in cats)
- Acid–base/lactate if the patient becomes unwell

## Toxicity and overdose

The serious toxicity is LACTIC ACIDOSIS — uncommon but potentially fatal, occurring chiefly with renal/hepatic impairment, dehydration or hypoperfusion. Overdose causes GI signs and, if acidosis develops, weakness, hyperventilation, hypotension and collapse. It does not cause hypoglycaemia on its own.

Management: No specific antidote. Supportive — IV fluids, correct acidosis, and monitor lactate/acid–base, renal function and glucose. Haemodialysis effectively removes metformin and corrects lactic acidosis in severe cases. Discontinue and address precipitating factors (dehydration, renal impairment).

## Clinical pearls

- Largely a human drug with marginal veterinary use — in cats it is usually disappointing (GI intolerance, poor efficacy) and insulin remains the standard for feline diabetes
- It improves insulin SENSITIVITY and suppresses hepatic glucose output (no insulin secretion → no hypoglycaemia alone) — hence interest in equine insulin dysregulation/EMS, though evidence and bioavailability are limited
- Respect the lactic-acidosis risk: avoid in renal/hepatic impairment, dehydration or poor perfusion
- Diet/exercise/weight management remain central to insulin-resistance conditions

## Mechanism of action

A biguanide that activates AMP-activated protein kinase (AMPK), primarily SUPPRESSING hepatic gluconeogenesis and increasing peripheral insulin sensitivity/glucose uptake, with reduced intestinal glucose absorption — lowering blood glucose without stimulating insulin secretion (hence no intrinsic hypoglycaemia). It mildly inhibits mitochondrial complex I, which shifts metabolism toward anaerobic lactate production — the basis of the rare lactic-acidosis risk in compromised patients.

## Formulations and products

- 250 / 500 mg tablet
- 850 / 1000 mg tablet (incl. SR)
- Glycomet — 250 / 500 / 850 / 1000 mg tablet (SR), Tablet (human-label)
- Glucophage — 500 / 850 / 1000 mg tablet, Tablet (human-label)

## Storage

Tablets: 15–30 °C, dry, protect from light/moisture.

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

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## Frequently asked questions

### What is the dose of Metformin for cats?

Reference doses for Metformin in cats: 25–50 mg per cat PO q12h (≈2–10 mg/kg) PO q12h (Type-2 diabetes (residual insulin; limited efficacy)). Confirm against the label and the patient before use.

### What is the dose of Metformin for horses?

Reference doses for Metformin in horses: 30 mg/kg PO q8–12h, 30–60 min before feeding (Equine metabolic syndrome — adjunct (Plumb’s 10e; controversial)). Confirm against the label and the patient before use.

### When should Metformin not be used?

Renal impairment (reduced clearance → lactic-acidosis risk), hepatic disease, hypoxaemia/poor tissue perfusion/dehydration (lactic-acidosis risk), and diabetic ketoacidosis (use insulin). Concurrent contrast agents/anaesthesia in compromised patients. Known hypersensitivity. Insulin-dependent diabetes (ineffective alone).

### What are the side effects of Metformin in animals?

GI upset (anorexia, vomiting, weight loss) — common in cats, often limiting; Lactic acidosis (rare but serious, esp. with renal/hepatic impairment or hypoperfusion); Does not cause hypoglycaemia alone (no insulin secretion).

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.