Metyrapone

What is metyrapone?

Metyrapone is an adrenal enzyme-blocking drug mainly used to treat cats with hyperadrenocorticism (Cushing’s disease). It is most useful as a short-term treatment to stabilize cats with Cushing’s disease before surgery. It may also be used in ferrets and hamsters.

There are no veterinary-labelled products. The human product (Metopirone®) may be prescribed for off-label use in pets.

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 directions and cautions carefully, as they may be significantly different from those on the label.

How do I give my pet metyrapone?

• Metyrapone is given orally (by mouth)
• This drug comes in capsule format.
• It may be given with or without food; however, giving it with food may prevent vomiting.
• If vomiting occurs when dosed on an empty stomach, give future doses with food or a treat.
• 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 days; however, its effects will not be noted outwardly, and laboratory tests may be required to evaluate this medication’s effectiveness.

What if I miss giving my pet the medication?

If you miss a dose, give it as soon as you remember. However, if it is almost time for the next scheduled 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 metyrapone?

Serious adverse reactions associated with this drug may occur without warning and could, in rare cases, lead to death. If any of the following signs develop, stop giving metyrapone and contact your veterinarian immediately:

• Vomiting
• Reduced appetite
• Seizures
• Weakness
• Collapse (passing out)
• Muscle twitching
• Depression
• Unsteadiness

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 metyrapone in:

• Pets that are allergic to it
• Pets with low levels of cortisol in the body (adrenocortical insufficiency, Addison’s disease)

USE WITH CAUTION in:

• Pets with diabetes mellitus
• Pets that are pregnant

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 NOT BE USED when given with metyrapone:

• Corticosteroids
• Acetaminophen

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

• Estrogen
• Phenytoin
• Insulin or other antidiabetic agents (may intensify side effects of metyrapone when used together)

Is any monitoring needed with this medication?

• Blood glucose testing should be performed regularly in cats with diabetes mellitus, to determine any needed changes in insulin dosage.
• ACTH stimulation tests may be used to assess adrenal function.
• 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.
• Your veterinarian will let you know when and how they want to reassess your pet to ensure the medication is working and not causing side effects.

How do I store metyrapone?

• Ensure metyrapone is tightly stored in its original container in a cool, dry place and protected from light.
• Store this medication at room temperature of 59°F–77°F (15°C–25°C)
• 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.