Can cats take metformin?

In this article:

• Metformin for cats
• Safety
• Dosage
• Alternatives
• Summary

In this article

• Metformin for cats
• Safety
• Dosage
• Alternatives
• Summary

Metformin hydrochloride treats Type 2 diabetes mellitus, the most common type of diabetes in people and cats. Although metformin is typically the first drug doctors use to treat Type 2 diabetes in people, veterinarians avoid it because it’s considered ineffective in most cats. Insulin and dietary management is the treatment of choice for all types of feline diabetes, though a few oral hypoglycemics can be used. It is possible that a veterinarian may try metformin, but the caregiver should ask about possible side effects and better treatment options.

RELATED: Save up to 80% on metformin

What is metformin used for in cats?

Metformin has been studied for use in cats with Type 2 diabetes. Veterinarians usually avoid metformin in cats. 

Diabetes

About 0.2% to 1% of cats are diagnosed with diabetes, a condition in which the cat loses the ability to produce or respond to insulin, a hormone that tells cells in the body to pull sugar (glucose) from the bloodstream. In cats with diabetes, blood sugar levels rise and stay high, the defining characteristic of diabetes. When blood sugar levels get high enough, the excess sugar starts to damage blood vessels. Over time, this damage slowly damages vital organs such as the kidneys, liver, pancreas, and eyes.

In humans, most diabetic patients have Type 2 diabetes, a condition in which the body loses the ability to respond to insulin. A minority of people have Type 1 diabetes, a condition that reduces the body’s ability to produce insulin. This is true in cats: most (90% of diabetic cats) have Type 2 diabetes, which veterinarians usually call “insulin-resistant diabetes.” Cats most at risk for developing insulin-resistant diabetes are those that are older, overweight, physically inactive, kept indoors, or treated with corticosteroids.

Most people with Type 2 diabetes are treated with oral hypoglycemics, drugs that lower blood sugar. Metformin is typically the first drug used. It works with minimal side effects. It’s a unique oral antidiabetic drug. As a biguanide, it increases the insulin sensitivity of the body’s cells. 

Veterinarians treat Type 2 feline diabetes with insulin and dietary changes. They don’t use metformin or most other oral antihyperglycemic drugs used in people. Instead, the treatment of choice is insulin and dietary changes. Although commonly used in people, metformin doesn’t work in most cats even though it has similar bioavailability and plasma concentrations that it has in people. For example, metformin achieved glycemic control in only 1 out of 5 cats in one key study, 

A veterinarian can prescribe metformin to cat owners who want to avoid insulin injections, but this is unlikely. If metformin is prescribed, ask the veterinarian about alternative oral medications and what to do if metformin doesn’t succeed.

Is metformin safe for cats?

Metformin is not usually prescribed to cats. It won’t work for most cats with Type 2 diabetes. There are also concerns about its safety. 

Metformin is contraindicated in cats with:

• Metabolic acidosis
• Kidney dysfunction
• Known allergies to metformin

Side effects of metformin in cats

The most common side effects of metformin in cats are:

• Inappetence
• Weight loss
• Low energy
• Vomiting

If these adverse effects persist or worsen, talk to the veterinarian.

The most serious reported side effects in cats include:

• Severe vomiting
• Severe diarrhea

Call a veterinarian or animal hospital if the cat has any of these side effects.

Because of metformin’s mechanism of action, hypoglycemia (low blood glucose) is uncommon with metformin therapy unless insulin is being used, as well.

In people, the most serious and potentially life-threatening side effect of metformin is lactic acidosis. Lactate builds up in the blood. As lactate concentrations rise, the blood becomes more acidic. Lactic acidosis usually results from prolonged metformin use at high doses, so it could happen if a cat is taking metformin over the long-term. 

Pet owners dosing their cat with metformin should call the veterinarian or a veterinary hospital if they notice clinical signs of lactic acidosis, such as:

• Fast breathing
• Lethargy
• Weakness
• Confusion
• Collapse 

Interactions of metformin with other pet meds

Metformin dosing has significant drug interactions, including: 

• Blood pressure drugs called ACE inhibitors
• Thiazide diuretics or furosemide
• Corticosteroids

If a veterinarian needs to take X-rays or similar images that require a contrast agent, metformin doses must stop at least two days before the procedure.

Metformin dosage for cats

Metformin has been studied in cats, although it’s not commonly used in clinical practice. Published research has documented two possible dosages for feline insulin-resistant diabetes:

• For insulin-resistant diabetes: 50 mg daily given in two divided doses OR 2 mg/kg given every 12 hours

Human formulations of metformin come in much larger dosage strengths than this. The smallest metformin tablet for people is 500 mg. These dosage strengths are too large to allow for accurate dosing. A veterinarian will have to supply a lower-dose tablet prepared by a compounding pharmacy.

Can cats overdose on metformin?

Cats can overdose on metformin, but there have been no reported fatalities. Most cats who overdose on metformin will show some symptoms, such as vomiting, stomach upset, or diarrhea. The most severe side effects of a metformin overdose are severe vomiting and diarrhea. 

In case of accidental ingestion or an overdose, call an animal poison control center or take the cat to a veterinary hospital.

Can I give my cat metformin every day?

Veterinarians do not usually consider metformin a viable treatment in diabetic cats. If it is prescribed, pet owners will give their cat metformin twice daily every day. In people, metformin is a long-term and even lifelong treatment. Veterinarians have not studied long-term metformin use in cats.

How to give your cat metformin

Metformin is not commonly given to cats, so there are few resources available to guide pet owners when giving doses. With little information, pet owners should strive to closely follow all the veterinarian’s instructions.

• Doses will probably be given twice a day, 12 hours apart.
• Do not give the cat doses that are larger than prescribed or give doses more frequently than prescribed.
• If giving a tablet to your cat is difficult, ask a veterinary assistant to demonstrate the most effective procedure.
• Do not miss doses. Ask the veterinarian what to do if a dose is missed. 
• Store metformin tablets at room temperature. Keep the tablets in a closed, light-resistant container.

Metformin alternatives for cats

Veterinarians rarely prescribe metformin for cats. When they do, it may not work.

The first-line treatments for feline diabetes are dietary changes and insulin treatment. Unfortunately, insulin treatment is difficult and often frustrating. About 1 in 10 pet owners choose to euthanize their cat before starting treatment. Another 1 in 3 diabetic cats are euthanized in the first year. 

Fortunately, there are alternatives to insulin. Metformin may not be an option, but other oral hypoglycemics do work. The FDA has approved two oral hypoglycemics for cats that can be used instead of insulin: Bexacat (bexagliflozin), a tablet, and Senvelgo (velagliflozin), an oral liquid. Both are administered once daily.

Bexacat and Senvelgo are sodium-glucose cotransporter 2 inhibitors (SGLT2 inhibitors). They work by increasing the amount of blood sugar excreted through the urine. They are both highly effective. In clinical trials, Bexacat successfully controlled blood sugar in 84% of treated cats. Senvelgo successfully controlled blood sugar in 89% of treated cats by day 30. 

Both drugs are safe for otherwise healthy cats that have never been treated with insulin. Neither drug is appropriate for cats with insulin-dependent diabetes mellitus. The most serious side effects include diabetic ketoacidosis and low blood sugar (hypoglycemia).

Glipizide is another possible treatment option. It is a sulfonylurea drug that works by increasing the body’s production of insulin. Glipizide is only appropriate if the cat is mildly hyperglycemic and producing insulin.

Summary

Veterinary literature discourages veterinarians from using metformin in cats. It’s not dangerous, but it’s rarely successful at treating blood sugar in insulin-resistant diabetic cats. If a veterinarian prescribes metformin, discuss possible side effects and next steps if the drug doesn’t work. There are other options besides insulin or metformin for treating Type 2 diabetes in cats.