Metformin

What is metformin?

Metformin is an oral drug used as an anti-hyperglycemic (a medication that counteracts the accumulation of excess sugar in the blood) in cats with non-insulin-dependent diabetes mellitus (NIDDM).

There is limited evidence to support the use of metformin in dogs with NIDDM, and the incidence of NIDDM is rare in dogs. Horses with insulin resistance associated with equine metabolic syndrome may benefit from metformin, but there is debate about its usefulness in this species.

There are no veterinary-labelled products. Human products may be prescribed for off-label use in pets (Glucophage®, Glucophage XR®, Glumetza®, Fortamet®, generics). A compounded formulation of metformin may be required to achieve therapeutic levels.

Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s direction and cautions carefully, as they may be significantly different from those on the label.

How do I give my pet metformin?

• Metformin is given orally (by mouth).
• Metformin comes as tablets, extended-release tablets, and oral solution. There are also fixed-dose oral tablet combination products available that contain metformin and glyburide or glipizide.
• This medication may also be compounded into other forms.
• Metformin may be given with or without food.
• If vomiting occurs when dosed on an empty stomach, give future doses with food or a treat.
• Measure liquid forms carefully.
• Follow the instructions on the product label, in conjunction with your veterinarian’s directions.
• Ideally give this medication at the same time daily.

This medication should take effect within 1 to 2 hours, but its effects may not be noticeable for a few days.

What if I miss giving my pet the medication?

If you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.

Are there any potential side effects from metformin?

Metformin may cause the following side effects:

• Mild diarrhea
• Mild vomiting
• Loss of appetite
• Mild lethargy
• Weight loss
• Unsteadiness
• Muscle twitching

Serious adverse reactions may occur. If any of the following signs develop, stop giving metformin and contact your veterinarian immediately:

• Prolonged vomiting and/or diarrhea
• Prolonged inappetence and weight loss
• Extreme lethargy
• Seizures
• Collapse

Drug sensitivities can develop over time, with repeated exposure. Your pet may have no reaction after the first few doses but may develop a sensitivity later. It is important to watch for signs of an allergic reaction over the entire course of the treatment and notify your veterinarian if you have any concerns.

Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately. This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

DO NOT USE metformin in:

• Pets that are allergic to it
• Pets with known kidney problems
• Pets that are suffering from ketoacidosis or any other form of acidosis

Are there any drug interactions I should be aware of?

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment.

The following drugs should be USED WITH CAUTION when given with metformin:

• Ace inhibitors
• Carbonic acid inhibitors (e.g., acetazolamide, zonisamide)
• Cimetidine
• Corticosteroids
• Digoxin
• Diuretics
• Fluroquinolone antibiotics (e.g., enrofloxacin)
• Furosemide
• Iodinated contrast agents (intravenously)
• Isoniazid
• Phenylpropalamine
• Ranitidine
• Trimethoprim

Is any monitoring needed with this medication?

• Baseline blood work is recommended before starting this medication to assess your pet's general health.
• Follow your veterinarian’s recommendations on the frequency of monitoring your pet’s health and laboratory testing.
• Follow your veterinarian’s monitoring recommendations for controlling your pet’s diabetic condition, including periodic checks of your pet’s physical status, body weight, blood glucose, blood work, and urinalysis. Your veterinarian may adjust the medication dose based upon these results and an assessment of how your cat is responding clinically.
• At home, monitor for any side effects such as those noted above. If any side effects occur, stop using the medication and contact your veterinarian.

How do I store metformin?

• Ensure metformin is tightly stored in its original container in a cool, dry place, protected from light. 
• Store this medication at room temperature of 68°F–77°F (20°C–25°C) for tablets, and 59°F–86°F (15°C–30°C) for oral solution. 
• Keep the container out of reach of children and pets.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility. Be prepared to provide information about the product and your pet’s weight and symptoms.