Insulin
Insulin is a critical peptide hormone produced by the beta cells of the pancreatic islets of Langerhans. It is the cornerstone of therapy for diabetes mellitus and diabetic ketoacidosis (DKA) in veterinary medicine. Formulations are broadly categorized by their onset and duration of action: * **Short-acting (Regular, Lispro):** Used primarily in hospital settings for acute stabilization of DKA or severe hyperkalemia. Regular insulin is the only formulation that can be administered intravenously. * **Intermediate-acting (NPH, Lente/Porcine Zinc):** Commonly used for maintenance therapy in dogs. Porcine insulin is structurally identical to canine insulin, minimizing the risk of anti-insulin antibody formation. * **Long-acting (PZI, Glargine, Detemir):** Frequently used for maintenance therapy in cats, who metabolize insulin more rapidly than dogs. > **Clinical Pearl:** Feline diabetes often resembles human Type 2 DM and may go into remission with early, aggressive use of long-acting insulins (like glargine) combined with a low-carbohydrate diet. Canine diabetes is typically akin to human Type 1 DM, requiring lifelong exogenous insulin therapy.
Mechanism: Insulin initiates its action by binding to the **tyrosine kinase insulin receptor** on the cell membrane. **Mechanism Pathway:** Receptor binding โ Autophosphorylation โ Activation of **Insulin Receptor Substrates (IRS)** โ Activation of the **PI3K/Akt pathway** โ Translocation of **GLUT4** transport proteins to the cell surface โ Rapid facilitated diffusion of glucose into skeletal muscle and adipose tissue. **Metabolic Effects:** * **Carbohydrate metabolism:** Promotes cellular glucose uptake and hepatic glycogenesis; inhibits glycogenolysis and gluconeogenesis. * **Lipid metabolism:** Stimulates lipogenesis and potently inhibits lipolysis and ketogenesis (crucial for resolving DKA). * **Protein metabolism:** Increases amino acid uptake and protein synthesis. * **Electrolyte shift:** Drives potassium and magnesium into the intracellular space (utilized therapeutically for life-threatening hyperkalemia).
Dosing by species
- Diabetic ketoacidosis (Regular insulin) ยท Same protocol using regular insulin as described for dogs ยท IM, IV, SC ยท Varies ยท Until stabilized
- Diabetic ketoacidosis (Glargine) ยท 2 Units per cat SC and 1 Unit per cat IM (regardless of body weight) initially; repeat the IM dose 4 or more hours later if BG > 250-290 mg/dL; repeat the SC dose every 12 hours. ยท SC and IM ยท Initially, then q12h SC ยท Until stabilized
- Severe hyperkalemia ยท 0.5 to 1 Unit/kg IM regular insulin plus 2 grams dextrose per unit of insulin IV ยท IM ยท Once
- Uncomplicated diabetes mellitus (Glargine, Detemir, or PZI) ยท Blood glucose <360 mg/dL: 0.25 Units/kg of ideal body weight SC every 12 hours; Blood glucose >=360 mg/dL: 0.5 Units/kg of ideal body weight SC every 12 hours ยท SC ยท q12h ยท Lifelong ยท If no monitoring in first week, begin with 1 Unit per cat every 12 hours.
- Uncomplicated diabetes mellitus (ProZinc) ยท 0.2-0.7 Units/kg SC every 12 hours given concurrently with or right after a meal ยท SC ยท q12h ยท Lifelong ยท Goal: glucose nadir between 80 & 150 mg/dL.
- Uncomplicated diabetes mellitus (Vetsulin) ยท 0.5 Units/kg SC once daily ยท SC ยท q24h ยท Lifelong
- Uncomplicated diabetes mellitus (Lente) ยท 1 Unit per cat SC twice daily for cats <4kg & 1.5-2 Units/cat twice daily for cats >4kg. Alternatively: 0.25 Units/kg SC twice daily if BG 216-342 mg/dL; 0.5 Units/kg SC twice daily if BG>360mg/dL. ยท SC ยท q12h ยท Lifelong
- Diabetes mellitus ยท 0.5-1 Unit per ferret SC twice daily. Alternatively: 0.1-0.5 Units/kg IM or SC twice daily to start; adjust to optimal dose. ยท SC, IM ยท q12h ยท Lifelong ยท May require insulin to be diluted.
Routes of administration
Contraindications
- Episodes of hypoglycemia (absolute contraindication)
- Systemic allergy to pork or pork products (specifically for Vetsulin/porcine lente)
Adverse effects
- Hypoglycemia (most common and potentially life-threatening)
- Insulin-induced hyperglycemia ('Somogyi effect' due to counter-regulatory hormone release following hypoglycemia)
- Insulin antagonism or resistance
- Rapid insulin metabolism
- Local hypersensitivity reactions to 'foreign' proteins
- Lipodystrophy at the injection site (if sites are not rotated)
Drug interactions
- Beta-adrenergic blockers (e.g., propranolol) ยท Can have variable effects on glycemic control and can mask the clinical signs associated with hypoglycemia.
- Clonidine, Reserpine ยท Can mask the signs associated with hypoglycemia.
- Digoxin ยท Insulin alters serum potassium levels; concurrent use requires close monitoring for cardiac arrhythmias, especially with concurrent diuretics.
- Alcohol, Anabolic steroids, ACE inhibitors, Aspirin, Disopyramide, Fluoxetine, MAOIs, Somatostatin derivatives, Sulfonamides ยท May potentiate the hypoglycemic activity of insulin.
- Calcium channel blockers, Corticosteroids, Danazol, Diuretics, Isoniazid, Niacin, Phenothiazines, Thyroid hormones ยท May decrease the hypoglycemic activity of insulin (cause insulin resistance).
Monitoring
- Blood glucose (serial curves or continuous monitoring)
- Patient weight
- Appetite and water intake
- Urine output
- Blood or urine ketones (if DKA suspected)
- Fructosamine (goal <450 micromol/L) or glycosylated hemoglobin
Overdose
Overdosage of insulin leads to **hypoglycemia**, which can be rapidly fatal or cause permanent brain damage if untreated. **Clinical Signs:** * Weakness, lethargy, ataxia * Shaking, muscle fasciculations * Head tilting, bizarre behavior, blindness * Restlessness, extreme hunger * Seizures and coma **Treatment:** * **Mild:** Offer the animal its usual food. * **Severe (e.g., seizures):** Rub oral dextrose solutions (e.g., **Karoยฎ syrup**) on the oral mucosa (do not pour down the throat to avoid aspiration). * **Veterinary Intervention:** Intravenous injections of 50% dextrose solutions (small amounts, slowly administeredโusually 2-15 mL). * **Monitoring:** Once alleviated (usually within 1-2 minutes), monitor closely with serial blood glucose levels to prevent recurrence (especially with long-acting insulins) and adjust future doses.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.