Altrenogest

Overview

Altrenogest is a synthetic oral progestin that mimics the physiologic effects of endogenous progesterone. In small animal practice, it is used extra-label in dogs for reproductive hormone support, particularly in cases of documented luteal insufficiency or for the prevention of premature parturition.

Progestins play a key role in maintaining pregnancy by stabilizing the endometrium, inhibiting uterine contractions, and supporting normal luteal function. Altrenogest exerts its effects through negative feedback on the hypothalamic–pituitary axis, reducing gonadotropin secretion and promoting maintenance of a progesterone-dominant state.

In dogs, altrenogest is administered orally and is systemically active. Because it is readily absorbed through the skin, strict handling precautions are required to minimize accidental human exposure. Its use should be limited to carefully selected patients, and underlying infectious or non-hormonal causes of reproductive failure should be ruled out before initiating therapy.

Indications

In small animal practice, altrenogest is used extra-label in dogs for specific reproductive indications related to progesterone deficiency. Its use should be reserved for cases in which hormonal insufficiency has been identified or strongly suspected.

• Luteal insufficiency: Used to support pregnancy in bitches with documented or suspected inadequate endogenous progesterone production during diestrus or early gestation.
• Prevention of premature delivery: Administered to help maintain uterine quiescence and reduce the risk of premature parturition when progesterone deficiency is considered a contributing factor.

Dosage (Reference)

Dog

In dogs, altrenogest is used extra-label for reproductive hormone support. Treatment is based on maintaining adequate progesterone activity in bitches with documented or suspected luteal insufficiency. Therapy should be carefully timed and monitored throughout administration.

Cat

There are no established or referenced dosage recommendations for altrenogest use in cats in the available source. As a result, routine use in cats cannot be recommended, and dosing guidelines have not been defined.

Warnings & Precautions

Altrenogest is a potent synthetic progestin and should be used with caution in small animal patients. Its use in dogs is extra-label and should be limited to clearly justified reproductive indications. Careful patient selection, monitoring, and strict handling precautions are essential.

• Confirmed luteal insufficiency: When used to maintain pregnancy, luteal insufficiency should be documented or strongly suspected, and infectious causes of pregnancy loss should be ruled out before initiating therapy.
• Pregnancy timing (dogs): Avoid administering altrenogest to pregnant bitches during the first trimester. Therapy should be discontinued 2–7 days prior to the anticipated whelping date.
• Reproductive tract disease: Progestin therapy may exacerbate underlying uterine disease; use cautiously in animals with a history of uterine pathology.
• Limited species data: Safety and efficacy have not been established in cats. Routine use in cats is not recommended due to lack of species-specific data.
• Human exposure risk: Altrenogest is readily absorbed through the skin and can penetrate porous gloves (e.g., latex). Individuals who are pregnant, may be pregnant, or have hormone-sensitive conditions should not handle this medication.
• Protective equipment: Impermeable gloves (e.g., nitrile or vinyl; NOT latex) should be worn when handling the drug to minimize dermal exposure.
• Accidental exposure: If skin contact occurs, wash immediately with soap and water. In case of eye exposure, flush with water for 15 minutes and seek medical attention. If swallowed, do not induce vomiting and seek medical care.
• Hazardous drug classification: Progestins are classified as hazardous drugs by the National Institute for Occupational Safety and Health (NIOSH); appropriate precautions should be followed during handling and administration.

Drug Interactions

The following drug interactions with altrenogest have been reported or are considered theoretical and may be clinically relevant in dogs. Concomitant use is not always contraindicated, but potential risks should be considered and additional monitoring performed when appropriate. There are no species-specific interaction data available for cats.

• Dinoprost: Altrenogest may reduce the therapeutic effects of dinoprost when used concurrently.
• Heparins (e.g., heparin, enoxaparin): Concurrent use of progestins may reduce the anticoagulant effects of heparin or low-molecular-weight heparins.
• Hypoglycemic agents (e.g., insulin, glipizide): Altrenogest may reduce blood glucose–lowering effects; monitor glycemic control closely in diabetic patients.
• Rifampin: May decrease progestin activity due to microsomal enzyme induction and increased metabolism of altrenogest.
• Phenobarbital: Concurrent administration may reduce the effectiveness of altrenogest through hepatic enzyme induction.

Side Effects & Overdose

Side Effects

Adverse effects associated with altrenogest appear to be uncommon when the drug is used at recommended dosages. Most reported effects are related to prolonged exposure to progestins and their influence on the reproductive tract.

• Uterine effects (dogs): Progestogens may induce cystic endometrial hyperplasia and increase the risk of pyometra in bitches, particularly with prolonged or repeated use.
• Reproductive hormone effects: Long-term progestin exposure may alter normal reproductive hormone balance and should be limited to clearly indicated cases.
• Cats: No specific adverse effect data are available for cats; safety has not been established in this species.

Overdose

Information regarding acute overdose in dogs and cats is limited. Experimental toxicity data suggest a wide safety margin; however, clinical effects following accidental overdose in small animals have not been well documented.

• Dogs: Dogs have tolerated oral doses up to 400 mg/kg in experimental settings, indicating a relatively low acute toxicity risk.
• Cats: No overdose or toxicity data are available for cats.
• Management: In suspected overdose cases, treatment is supportive. Consultation with a veterinary poison control center is recommended for guidance and monitoring.

Key Notes

Practical clinical considerations to guide the appropriate use of altrenogest in small animal reproductive management:

• Extra-label use: Altrenogest is not FDA-approved for use in dogs or cats; its administration should be based on informed clinical judgment and documented justification.
• Diagnostic confirmation: Hormonal therapy should be part of a diagnostic-driven approach, not used empirically without evaluating other causes of reproductive failure.
• Duration of therapy: Progestin treatment should be limited to the shortest effective duration to reduce the risk of hormonally mediated uterine pathology.
• Monitoring response: Clinical response should be assessed through pregnancy monitoring and overall reproductive outcome rather than behavioral signs alone.
• Client counseling: Owners should be informed that this medication alters reproductive hormones and is intended strictly for specific reproductive indications, not routine use.
• Handling awareness: Clinics should establish clear protocols for safe storage and handling due to the drug’s hormonal activity and occupational exposure risks.
• Cats: Lack of species-specific data limits clinical application; use should be approached with caution and avoided in the absence of supporting evidence.