Major Uses

Altrenogest is used to suppress estrus or to control the time that estrus starts in mares to facilitate scheduled breeding.

Common Precautions

Side effects are rare if Atrenogest is given at the labeled dosages, but slight changes in blood levels of potassium, calcium, or liver enzymes may be visible. Altrenogest should not be used in mares with uterine infections or endometritis. Pregnant or male horses should not take Altrenogest. Humans handling Altrogestin, particularly women, must avoid contact with skin. In order to evade absorption through skin, handlers should wear impervious protective gloves.

Altrenogest should not be administered to animals with a known allergy or hypersensitivity to the drug. Emergency veterinary care should be sought if an animal experiences facial swelling, hives, sudden onset of diarrhea, scratching, shock, seizures, cold limbs, pale gums, or coma.


Altrogenest should be stored at room temperature in a tightly closed container.


Altrenogest is available in an oil solution of 0.22 percent (2.2 mg/mL).

A typical dose for Altrenogest in horses is 1 mg/kg (or 1 mL per 110 pounds) once per day for fifteen days. It is to be administered orally in the mare's food, or directly onto the tongue using a syringe. 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 instructions and/or those printed on the medication label should be followed closely.

If a dose is missed, it should be given as soon as remembered. If it is almost time to give the next dose, the missed dose should be skipped and the regular administration schedule resumed. An animal should not receive two doses simultaneously.

This information is for general reference only and should not be used for the diagnosis or treatment of any condition of your pet. It's intended as a general reference, this information may not include all possible uses, precautions, directions, reactions (including allergic), drug interactions, or withdrawal times. Always consult your local veterinarian and have your pet examined for any advice concerning the diagnosis and treatment of your pet, including which products and doses are most appropriate. Any trademarks are the property of their respective owners. VetDepot is not a pharmacy. All prescription products are dispensed by our Pharmacy Partner. Article last updated 2/2014.