Megestrol Acetate

Major Uses

Megestrol acetate belongs to the class of drugs called progestins. It is very similar to the naturally occurring hormone progesterone and demonstrates steroidal effects and anti-estrogen properties. It also affects the function of the adrenal glands.

Megestrol acetate is used to treat dogs suffering from certain reproductive problems, to treat false pregnancies, and to control heat cycles, and it is used as an extra-label treatment of behavioral and skin problems in cats. This drug may also be used to treat benign prostatic hypertrophy.

Common Precautions

Side effects are varied and may include listlessness, mammary enlargement, lactation, temperament changes, and increased appetite. Pyometra is a rare, but possible, side effect.

Megestrol acetate should not be used in pregnant animals or in those with diabetes, uterine disease, or mammary tumors. Repeated use of the drug to control heat cycles in cats and dogs increases the risk of future problems, such as infections of the uterus. Because this medication has profound effects on adrenal gland function, animals undergoing treatment with megestrol acetate must be closely monitored. Insufficiency of the adrenal gland may occur after only a few weeks of treatment with megestrol acetate.

Cats are at risk of developing transient diabetes mellitus following use of megestrol acetate. Use of the drug may also be associated with liver disease in cats. Because of these risks, extra-label use of megestrol in cats is no longer common.

Megestrol acetate is known to interact with certain other medications, including steroids and some antibiotics. Megestrol acetate should not be used in animals with a known allergy or hypersensitivity to the drug. Any known or suspected overdose should be reported to a veterinarian right away.

Storage

Megestrol acetate should be stored at room temperature. The drug should be kept away from heat sources and out of the reach of children and animals.

Administration

Megestrol acetate is available as tablets in strengths of 5 mg, 20 mg, and 40 mg.

To treat false pregnancy or control heat cycles in dogs, megestrol acetate is typically dosed at 0.25 mg/lb (0.5 mg/kg) once a day for 8 days. To suppress heat cycles in cats, the typical dose is 5 mg per cat per day. For the treatment of skin and behavioral problems in cats, megestrol acetate is typically dosed at 2.5 to 5 mg per cat per day.

Doses may vary in different species, when the drug is given by a different route or concurrently with other medications, and with regards to a patient's age, breed, and health status. A veterinarian's dosing instructions and/or those printed on the medication label should be followed closely.

If a dose of this medication is missed, a veterinarian should be consulted. A new dosing schedule may be required.