What is megestrol acetate?
Megestrol acetate (MA) (brand names: Ovaban®, Megace®) is a synthetic progestin: a hormone used to postpone estrus (heat cycle) and to relieve the effects of false pregnancy. It can also be used to treat benign prostatic hypertrophy in male dogs and to treat skin and behavior conditions in cats.
Its use in cats and male dogs to treat various conditions is “off label” or “extra label”. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.
How is megestrol acetate given?
- Before your pet receives this medication, they should be carefully evaluated, including a reproductive/heat cycle history, a complete physical exam, a check for breast tumors, and a vaginal smear.
- This medication is given by mouth in the form of a tablet or liquid.
- It may be given with or without food, but if vomiting occurs after giving on an empty stomach, give future doses with a meal or a treat.
- Megestrol is considered a hazardous drug. Wear gloves when handling the medication, and DO NOT HANDLE IF YOU ARE PREGNANT or NURSING. Wash your hands immediately after administering.
This medication can take up to a few weeks before the full effects are noted. However, improvement in clinical signs may not be visibly noticeable and so laboratory tests may be needed 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, 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?
Side effects in dogs may include:
- increased appetite
- weight gain
- lethargy
- behavior changes
- hair coat changes
More serious side effects in dogs include:
- inflammation or infection of the uterine tissues, which may cause vaginal discharge
- breast tissue enlargement
- breast tumors
- acromegaly (increases in soft tissue mass, skin folds, abdominal enlargement)
- adrenal gland suppression
- increased drinking and/or urination
- lactation (milk production)
Side effects in cats may include:
- increased appetite
- weight gain
- lethargy
- behavior changes
More serious side effects in cats include:
- severe lethargy
- vomiting
- diarrhea
- shaking
- collapse
- seizures
- increased drinking and increased urination
- changes in personality
- weight loss
- vaginal discharge
- breast tissue enlargement
- breast tumors
In cats that have chronic viral infections, this medication can cause a recurrence of the viral disease.
Rarely, liver toxicity can occur, and may cause yellowing of the skin, eyes, and gums, as well as decreased or lack of appetite.
Other side effects may also occur. If you notice anything unusual, contact your veterinarian immediately. This long-acting medication lasts for at least four to six weeks and may last longer in pets with kidney or liver disease.
Are there any risk factors for this medication?
Megestrol acetate should NOT BE USED in pets that:
- are allergic to it
- have uterine disease or uterine bleeding
- have diabetes mellitus
- have breast tumors
- have blood clots
- are pregnant
This medication should be USED WITH CAUTION in:
- lactating pets, as this medication enters the milk and the effects are unknown
- cats with known viral infections
- dogs with abnormal cycles
Other warnings:
- Do not use this medication to induce a heat cycle or in dogs prior to their first heat cycle.
- Avoid mating dogs that have a heat cycle within 30 days of completing megestrol acetate therapy.
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.
The following medications should be used with caution when given with megestrol acetate:
- corticosteroids
Is any monitoring needed with this medication?
The following monitoring is required while your pet is using megestrol acetate:
- blood glucose levels
- weight
- development of extra breast tissue or tumors
- vaginal discharge
- adrenocortical function
- liver enzymes
Your veterinarian will also monitor your pet to be sure that the medication is working.
At home, monitor for any side effects such as those noted above. If any side effects occur, discontinue the medication and contact your veterinarian.
How do I store megestrol acetate?
- Store tablets at temperatures less than 40°C (104°F), preferably between 2°C and 30°C (36°F and 86°F), in a tight container away from moisture.
- Store liquid between 15°C and 25°C (59°F to 77°F) in a tight container and protected from heat.
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.
