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Glargine Insulin for Dogs and Cats

By Barbara Forney, VMD

Last reviewed: 7/13/2022

Commonly prescribed for: Diabetes Mellitus

Species: Dogs and Cats

Therapeutic Class: Synthetic Insulin Analogue

Basic Information

Glargine insulin is a synthetic insulin analogue that is used in human medicine as a long-acting, "peak-less" insulin. It is administered subcutaneously once a day in humans and maintains a constant systemic absorption profile for 24 hours. Additionally, a short-acting insulin may be used before meals to further optimize glycemic control.

Glargine insulin is completely soluble at a low pH. When it is injected subcutaneously it forms a microprecipitate in the subcutaneous space. This allows for relatively constant and prolonged absorption. Glargine insulin cannot be mixed with other insulin because it would change the pH and the mechanism of absorption.

Dogs and Cats

Diabetes Mellitus is a relatively common metabolic disease seen in middle aged cats and dogs. Most dogs suffer from Type 1 diabetes, while cats usually have Type 2 diabetes. Type 3 diabetes may occur in either cats or dogs. In addition to treatment with insulin, the veterinary management of diabetes requires owner education, dietary management, and regular glucose testing. With appropriate management, most animals can live a normal lifespan.

In healthy cats, the duration of action for glargine insulin is 23 +0.9 hours. Diabetic cats may be maintained on once-a-day injection, although some cats may be better controlled with twice-a-day injection. It appears that glargine insulin is particularly useful in the treatment of the newly diagnosed, diabetic cat as some of these cats are able to achieve a diabetic remission.

Glargine insulin has not been as well studied in the dog as it has in the cat.

Side Effects

Hypoglycemia: The initial signs of hypoglycemia include nervousness, vocalization, anxiety, muscle tremors, ataxia, and pupillary dilation. The alert owner may be able to offer the patient some food or oral dextrose to counteract the hypoglycemia. Positive response should occur within one or two minutes. More severe signs of hypoglycemia include seizures, shock and coma. These animals require prompt veterinary intervention.


  • Urinary-tract infections are a common secondary problem in cats with diabetes.
  • Intact female cats should be neutered because the increased progesterone with diestrus makes the management of diabetes more difficult.
  • Dietary changes can affect insulin requirements.
  • Insulin may be used in pregnant animals, although breeding animals with diabetes is generally discouraged. Insulin may be used in lactating animals.
  • Injection-site reactions may occur. It is important to use multiple sites.

Drug Interactions

There are multiple drug-interactions with insulin.

  • Drugs that may increase the hypoglycemic activity of insulin include: captopril, enalpril, alcohol, anabolic steroids, beta-adrenergic blockers, MAOI’s, guanethidine, phenylbutazone, sulfinpyrazone, sulfonamides, tetracycline, and aspirin or other salicylates.
  • Drugs that may decrease the hypoglycemic activity of insulin include: dextrothyroxine, dobutamine, epinephrine, estrogen/progesterone combinations, furosemide, glucocorticoids, isoniazide, phenothiazine derivatives, and thiazide diuretics.
  • Thyroid hormones may increase blood glucose levels. When thyroid hormone is begun in a diabetic, hypothyroid patient, additional monitoring should be considered.
  • Topical glucocorticoids can alter glucose levels in the diabetic patient and should be avoided if possible.
  • Insulin can change serum potassium levels. Patients receiving digoxin and those on diuretics should receive additional monitoring of serum potassium levels.


Overdose with insulin will lead to varying degrees of hypoglycemia. Description of mild hypoglycemia is included with the side effects. More severe hypoglycemia can lead to seizures, blindness, cerebral edema, permanent brain damage, coma, and death.
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