by Jennifer Prince, DVM 
Drs. Foster & Smith
Veterinary Services Department

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Insulin is used in the treatment of diabetes mellitus. It comes in various forms and strengths, with corresponding syringes for each strength. The proper dose of insulin must be determined through monitoring blood glucose. The amount and time of insulin administration, the type of food, feeding time, and exercise must be consistent every day. An overdose of insulin can cause hypoglycemia (low blood sugar), with symptoms of weakness, trembling, unresponsiveness, seizures, coma, and death. If your pet experiences hypoglycemia, contact your veterinarian and feed the pet a normal meal, a sugary food, or place a small amount of sugar water or maple/karosyrup on the gums. 

Generic Name 

Brand Names 
Humulin, Iletin, Lente Iletin, NPH, and PZI 

Type of Drug 

Form and Storage 
Store in the refrigerator. 

Indication for Use 
Treatment of diabetes mellitus. 

For more information on diabetes mellitus and the use of insulin in treatment,
see Diabetes Mellitus in Cats: Causes and Characteristics. 

General Information 
Not FDA approved for use in dogs and cats but it is a common and accepted practice to use insulin in dogs and cats. Available over the counter but have your veterinarian call in a prescription the first time so the proper type of insulin and appropriate syringes are received. Diabetes mellitus results when the pancreas quits producing insulin or the body becomes resistant to the insulin and needs it in a higher quantity. Insulin is needed by the body to drive the glucose (blood sugar) into the cells where it is used for energy. When the glucose stays in the blood rather than go into the cells, the cells keep telling the body it needs more glucose so the body keeps producing it which causes the levels in the blood to rise. When it reaches a certain point, the glucose is passed out of the body through the urine. The glucose takes water with it producing more urine and causing the pet to drink more. If the diabetes is not controlled, it results in dehydration, weight loss, ketoacidosis (too much acid in the blood), coma, and death. Treatment consists of replacing the insulin from the pancreas with insulin that is injected under the skin which the body then absorbs. It may take multiple trips to the veterinarian and multiple blood tests to get the pet regulated, but pets may live for years if treated. Dogs and most cats need insulin injections for life while some cats are more difficult to treat as they may alternate between a diabetic state requiring insulin injections and a normal state not requiring insulin injections. They require more time and commitment by the owner. 

The only way to know how the body is responding to the insulin is by taking blood glucose levels over the course of the day. Fructosamine levels can be taken every several weeks to determine long term response especially in cats that have high glucose readings due to the stress of drawing blood. Urine glucose levels can be used to monitor glucose levels at home if needed. Contact your veterinarian for specifics on monitoring. 

Human insulin is the most commonly available insulin because that is what humans use. Most dogs do well on human forms of insulin. Cats do better on beef and/or pork insulin but PZI which is beef/pork insulin has been removed from the market. It is available on an investigational basis. Cats typically need a larger amount of the human based insulin than the beef/pork based. 

Insulin is available as regular (short-acting), NPH and Lente (intermediate-acting), and Ultralente and PZI (long-acting). Regular insulin is usually used in a veterinary hospital to get the pet's glucose level down before starting on an intermediate- or long-acting insulin that will be sent home with the pet. 

Usual Dose and Administration 
Doses vary considerably between patients. Usually start at 0.25-1.0 unit per pound daily in dogs and 1-3 units per cat daily. Insulin is given by a subcutaneous (SQ/under the skin) injection. Doses may need to be given twice a day. Doses may need to be much higher to get the diabetes under control and then decreased. Doses may need to be increased over time. Alter the injection site to decrease irritation to the tissue. 

Roll the bottle or turn it end over end to mix the insulin as it settles out in the bottom of the bottle between treatments. Do not shake the bottle as that will cause air bubbles to form, and it will be more difficult to get an accurate measurement. The insulin should be uniformly cloudy in the bottle when you draw it into the syringe. Draw the insulin into the syringe once and inject it back into the bottle. Redraw it into the syringe. This is helpful in accurately dosing as insulin may stick to the inside of the plastic syringe or an air bubble may be present in the syringe. 

Side Effects 
May see hypoglycemia (low blood sugar level) with symptoms such as weakness, lethargy, shaking, seizures, or coma. Cats may just sit and do nothing. May also see an insulin-induced hyperglycemia (too much sugar in the blood) where the body increases the blood sugar level because it had dropped too low. 

Do not change the pet's food, feeding schedule, or exercise schedule once regulated for that food and schedule. 

Avoid semi-moist food due to the high sugar content. 

Females should be spayed as estrus will change insulin requirements. 

Know which formula of insulin is being given and which syringes need to be used. The syringes come in U-100 and U-40 size that corresponds to the amount of insulin per milliliter (100 units per ml or 40 units per ml). (A milliliter (ml) and a cubic centimeter (cc) are the same.) Take a syringe and the bottle of insulin to the pharmacy when a refill is needed to make sure you have the correct supplies. Let the pharmacist know the amount you give and he can help you determine the size (such as 3/10cc or 5/10cc) of the syringe to get. 

Dogs that are poorly regulated have a greater risk of developing cataracts. 

Drug or Food Interactions 
Increased risk of hypoglycemia if used with anabolic steroids, beta-blockers, monoamine oxidase inhibitors, phenylbutazone, sulfinpyrasone, tetracycline, or salicylates like aspirin. 

Increased risk of hyperglycemia if used with glucocorticoids, thyroid medications, dobutamine, epinephrine, estrogen/progesterone combinations, or diuretics. 

Hypoglycemic agents such as glipizide may help lower insulin requirements as may chromium picolate. 

Use care when starting treatment for thyroid disorders in a diabetic animal as insulin needs may change. 

Changes in potassium levels may occur when using insulin, heart medications, and/or diuretics. 

In general, if the pet is on 1 injection a day, it should receive at least 2 meals: one at the time the insulin is administered and again at the time of day when the blood glucose is at its lowest level. If a pet receives 2 injections a day, generally feed at the time of each injection. If your pet does not eat, contact your veterinarian before giving the insulin. 

Hypoglycemia. Signs include weakness, trembling, unresponsiveness, seizures, coma, and death. In case the pet is given a double dose of insulin or is showing signs of low blood sugar, contact your veterinarian and feed the pet a normal meal, a sugary food, or place a small amount of sugar water or maple/karosyrup on the gums. Do not put anything in the mouth of an unresponsive patient. Do not get bit treating the pet. Contact your veterinarian or the Animal Poison Control Center if you think your pet may have accidentally received or been given an overdose of the medication. 

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