Metformin
**Metformin** is a biguanide oral antihyperglycemic agent widely used in human medicine for the management of type 2 diabetes. In veterinary medicine, its use is highly controversial and generally considered to have limited efficacy. * **Cats**: Investigated as an adjunctive treatment for non-insulin-dependent diabetes mellitus (NIDDM). However, clinical success is very limited, and the drug is often poorly tolerated due to gastrointestinal toxicity. Some veterinary endocrinologists strongly advise against its use in felines. * **Horses**: Researched for the management of Equine Metabolic Syndrome (EMS) and insulin dysregulation. Unfortunately, metformin has a highly unfavorable pharmacokinetic profile in horses, characterized by extremely low oral bioavailability (~4-7%) and a very rapid elimination half-life, making systemic efficacy questionable. > **Clinical Pearl**: Unlike sulfonylureas (e.g., glipizide) or insulin, metformin does not stimulate pancreatic insulin release and therefore rarely causes hypoglycemia when used as a sole agent.
Mecanismo: Metformin acts primarily as an **insulin sensitizer** and inhibitor of hepatic glucose output. Its actions are multifaceted: * **AMPK Activation**: Metformin activates **AMP-activated protein kinase (AMPK)** in hepatocytes → **decreases hepatic gluconeogenesis** (glucose production). * **Peripheral Sensitization**: Increases insulin's ability to transport glucose across cell membranes in skeletal muscle → **increases peripheral glucose uptake**. * **Intestinal Absorption**: May decrease the intestinal absorption of dietary glucose. * **Advanced Glycosylation**: Inhibits the formation of advanced glycosylation end-products. Because it does not stimulate insulin production or release from pancreatic beta cells, it does not directly induce hypoglycemia.
Dosificación por especie
- Non-insulin dependent diabetes mellitus (NIDDM) · 50 mg (total dose) per cat PO twice daily · PO · q12h · May be efficacious only in cats with detectable concentrations of insulin at time of treatment.
- Early NIDDM · 2 mg/kg PO q12h · PO · q12h
- General Use Warning · Not recommended · PO · Author states 'metformin has been shown toxic to cats and should not be used. It is also ineffective.'
- General · 100-500 mg/L of drinking water · PO · Continuous
Las dosis son una referencia clínica para médicos veterinarios. Confirme siempre con la información vigente del producto y el paciente individual.
Vías de administración
Contraindicaciones
- Hypersensitivity to metformin
- Renal dysfunction
- Metabolic acidosis
- Concurrent use of parenteral iodinated contrast agents (temporary contraindication)
Efectos adversos
- Lethargy
- Inappetence
- Vomiting
- Diarrhea
- Weight loss
- Lactic acidosis (rare but severe)
Interacciones farmacológicas
- ACE Inhibitors · May increase risk for hypoglycemia
- Cimetidine · Can cause a 60% increase in peak metformin plasma levels and a 40% increase in AUC
- Corticosteroids · May reduce hypoglycemic efficacy
- Diuretics, Thiazide · May reduce hypoglycemic efficacy
- Furosemide · Can increase the AUC and plasma levels of metformin by 22%; metformin can decrease the peak plasma concentrations and AUC of furosemide
- Iodinated Contrast Agents (Parenteral) · May cause acute renal failure and lactic acidosis if used within 48 hours of a metformin dose
- Isoniazid · May reduce hypoglycemic efficacy
- Sympathomimetic Agents · May reduce hypoglycemic efficacy
Monitoreo
- Fasting blood glucose
- Appetite and attitude
- Body condition
- PU/PD resolution
- Serum fructosamine and/or glycosylated hemoglobin levels
- Renal function (baseline and annually)
- Adverse effects (especially GI signs)
Sobredosis
**Overdose & Toxicity Profile:** * **Small Animals**: Hypoglycemia is **not commonly seen** in overdoses of metformin alone. However, the drug has a narrow margin of safety regarding gastrointestinal upset. * **Clinical Signs**: Vomiting and diarrhea are the most common findings in dogs and cats following accidental ingestion. * **Human Data**: Massive overdoses (e.g., 100 grams) caused hypoglycemia only 10% of the time, but **lactic acidosis** occurred. Lactic acidosis has been seen in human overdoses of 7 to 20 grams. It is unknown at what exact dose acidosis may occur in domestic animals. > **Management**: Treatment is largely supportive and symptomatic, focusing on managing GI distress and monitoring acid-base status and renal function.
La referencia de fármacos de VetSheet está destinada a médicos veterinarios como apoyo a la decisión clínica; no sustituye el juicio profesional ni la información vigente del fabricante.