Progesterone - Altrenogest

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pro-JES-tah-rone, al-TREN-o-jest - Pronunciation guide

Brand Names

  • Matrix
  • Regu-Mate Solution


Rx symbolProgesterone, along with altrenogest, which is a synthetic progestin, is used extensively in the reproductive management of mares to control the reproductive cycle, help maintain pregnancy, and help with behavior modification.


Progesterone may be used to prevent mares from coming into heat, to synchronize estrus cycles for better breeding efficiency, to organize or regulate heat cycles during the mare's seasonal transition, and to help maintain pregnancy. Progesterone is also used to modify estrus-related behaviors that interfere with performance and pleasure riding in non-breeding mares, and sometimes in stallions.

Dosage and Administration

Prescription medicationProgesterone
Method Dosage
(click row for calculator)
Concentration Period Duration
Oral 0.044 mg/kg 2.2 mg/ml Daily 15 days


    Skin contact must be avoided as Regu-Mate® (altrenogest) Solution 0.22% is readily absorbed through unbroken skin. Protective gloves must be worn by all persons handling this product. Pregnant women or women who suspect they are pregnant should not handle Regu-Mate® (altrenogest) Solution 0.22%. Women of child bearing age should exercise extreme caution when handling this product. Accidental absorption could lead to a disruption of the menstrual cycle or prolongation of pregnancy. Direct contact with the skin should therefore be avoided. Accidental spillage on the skin should be washed off immediately with soap and water.
  • Federal law restricts this drug to use by or on the order of a licensed veterinarian.
  • Extra-label use of drugs in treating animals is allowable only by licensed veterinarians within the context of a valid veterinarian-client-patient relationship, and does not include drug use in treating animals by the layman (except under the supervision of a licensed veterinarian).
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your equine appears to feel better, the entire treatment plan should be completed to prevent relapse.
  • This medication may be available in forms and concentrations not noted in the above table. Always check the label and literature provided with the medication about the form and concentration and DO NOT USE the calculator if the information differs.
  • Calculator is for educational purposes only. Follow your veterinarian's instructions regarding use of this, or any medication.

Side Effects

There are no known side effects for altrenogest when used according to directions. The most common side effect of progesterone in oil is an injection site reaction, such as pain or swelling. These reactions usually respond to hot compresses and NSAIDs.


Altrenogest has very serious potential side effects that can occur in humans who handle or administer the drug. Read package inserts carefully for handling instructions. Protective gloves should be worn at all times when handling this product.

Progesterone compounds, including altrenogest, should not be used in mares with chronic uterine infections.

Long-term use of progesterone compounds may delay return to normal reproductive cycles in mares.

Altrenogest is FDA approved for use with horses. Progesterone in oil is not FDA approved, but is commonly used and is accepted practice. Both drugs are prescription drugs. U. S. federal law restricts these drugs to use by or on the lawful written or oral order of a licensed veterinarian.

Progesterone compounds would be forbidden in any drug-free competition. Altrenogest is permitted in mares in some competitions. It is important to check with the appropriate regulatory group.


Rifampin may increase the speed of metabolism of progesterone compounds.


No information on overdose is available in the literature available.


Matrix Altrenogest Oral (swine)Matrix Altrenogest Oral (swine)

Regu-Mate SolutionRegu-Mate Solution



About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.