Altrenogest / Regu-Mate (Equine)
Generic: Altrenogest
Altrenogest, commonly known as Regu-Mate, is a potent synthetic progestin used in horses to suppress estrus, synchronize breeding cycles, and maintain pregnancy in mares prone to early embryonic loss.
This medication is intended for horses.
Overview
Altrenogest is a synthetic progestogen that effectively mimics the activity of natural progesterone, the primary hormone responsible for maintaining the equine reproductive cycle. In veterinary practice, it is primarily utilized to suppress the behavioral signs of heat, or estrus, in cycling mares. By providing a steady, exogenous source of progestogen, it inhibits the release of gonadotropins from the pituitary gland, thereby preventing the development of follicles and the subsequent exhibition of estrus behaviors that can interfere with performance or training schedules. While some endocrine disorders in other species may require specialized management with medications like Trilostane or Leuprolide, equine reproduction relies heavily on the precise regulation offered by altrenogest. When balancing metabolic endocrine health, veterinarians might also evaluate conditions requiring Levothyroxine (Equine) to ensure the mare is in optimal condition for reproductive success. Unlike treatments for hyperthyroidism in other species, such as Carbimazole, altrenogest focus is strictly on the reproductive axis. In cases where dopamine antagonism is required for pituitary conditions, a veterinarian may compare the physiological impact of altrenogest with Pergolide (Equine) to ensure patient safety. Reproductive timing is critical, and clinicians must differentiate between the needs of horses and smaller animals, which might otherwise require insulin analogs such as Insulin (Caninsulin/Vetsulin) or Detemir Insulin (Levemir) for glycemic control. Proper diagnostic screening prior to administration is essential, as the medication's impact on the hypothalamic-pituitary-ovarian axis is profound and requires veterinary oversight to monitor long-term safety and efficacy.
What It Treats
- Estrus Suppression: Used to stop estrus behavior in show mares during training or competition.
- Estrus Synchronization: Facilitates the grouping of mares for breeding programs, allowing multiple mares to enter estrus simultaneously.
- Maintenance of Pregnancy: Assists in sustaining pregnancies in mares with a history of luteal insufficiency or early embryonic loss.
- Transitioning Mares: Helps mares move from the anestrous winter period into the breeding season by managing follicular development.
How It Works
Altrenogest functions as an orally active progestin that exerts strong inhibitory control over the mare's hypothalamic-pituitary-ovarian axis. By maintaining elevated levels of progestin in the blood, the medication effectively tells the brain that the mare is in a luteal phase (or pregnant), which suppresses the surge of Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH). Without these surges, the mare does not undergo ovulation or express the behavioral signs of estrus. This 'artificial' luteal phase allows the veterinarian to control exactly when the mare will enter heat once the medication is withdrawn, as the drop in hormone levels triggers the natural onset of the next cycle. In clinical applications for maintaining pregnancy, the medication provides essential hormonal support when the mare's own corpus luteum may be failing to produce sufficient progesterone, thereby creating a stable hormonal environment for the fetus.
Dosage
The standard dose for suppressing estrus is 0.044 mg/kg (1 mL per 110 lbs of body weight) administered orally once daily. When using for synchronization, the duration of treatment is typically 10 to 15 days, followed by the administration of a prostaglandin to induce luteolysis. Always follow the precise dosage and duration prescribed by your veterinarian, as individual reproductive needs vary significantly.
Administration
The medication is typically provided as an oral solution or, in some cases, as a top-dress powder. It should be administered daily at the same time for the prescribed period. For liquid forms, a calibrated syringe is used to deposit the medication directly onto the back of the tongue or mixed into a small amount of feed, ensuring the entire dose is consumed. Because of the risk of absorption through the skin, the person administering the drug should always wear impermeable gloves and wash their hands thoroughly immediately after dosing.
Storage
Store the medication at controlled room temperature, typically between 15°C and 30°C (59°F to 86°F). Keep the container tightly sealed and away from direct sunlight or extreme temperature fluctuations. The product should be kept in its original packaging and stored in a secure location out of reach of children and pets, as accidental exposure can have significant hormonal effects on humans.
Contraindications
Altrenogest should not be used in mares with a known history of uterine infections or chronic endometritis, as the progestin-induced suppression of the uterus can exacerbate existing infections by preventing the natural clearance of uterine fluids. It is also contraindicated in stallions or mares with known hypersensitivity to the drug. Caution is required in animals with pre-existing liver disease, as the liver is the primary site of metabolism for synthetic progestins. Pregnant women should handle the medication with extreme caution, wearing protective gloves at all times, as the drug is absorbed through the skin and can cause severe hormonal disruption, including the risk of miscarriage or premature labor.
Interactions
Known drug interactions are relatively limited, but caution should be exercised when administering rifampin or other liver enzyme-inducing drugs, as these can accelerate the metabolism of altrenogest, reducing its efficacy. Additionally, the concurrent use of prostaglandin analogs (like cloprostenol or dinoprost) is standard for synchronization protocols, but should only be performed under strict veterinary guidance to ensure the correct timing of the follicular phase transition. There is little data on the interaction between altrenogest and long-term medications such as those used for PPID; however, any medication affecting pituitary or hypothalamic function should be reviewed by a specialist prior to the start of altrenogest.
Side Effects
- Rare cases of uterine infection (endometritis)
- Hormonal imbalances if used incorrectly
- Potential for prolonged estrus following withdrawal
- Skin irritation upon direct contact (due to rapid absorption)
- Rare allergic reaction or hypersensitivity
Sources & References
Frequently Asked Questions
This information is educational only and not a substitute for professional veterinary advice. Always consult a licensed veterinarian before starting or changing any medication.
