Altrenogest
Altrenogest is a synthetic oral progestational agent (progestin) widely used in veterinary reproductive medicine. - **Horses**: Indicated to suppress estrus in mares to allow predictable cycling, synchronize estrus, and maintain pregnancy in mares with luteal deficiency or placentitis. - **Swine**: Used to synchronize estrus in sexually mature gilts. - **Dogs**: Used off-label for luteal insufficiency and as a tocolytic treatment to prevent premature delivery. > **Clinical Pearl**: Altrenogest is highly lipophilic and readily absorbed through intact human skin. It poses significant health risks to handlers, particularly pregnant women and individuals with a history of thromboembolic or estrogen-dependent diseases.
กลไกการออกฤทธิ์: Altrenogest acts as an agonist at **progesterone receptors**. - Transforms proliferative endometrium into secretory endometrium. - Enhances myometrial hypertrophy and inhibits spontaneous uterine contractions (tocolytic effect). - Exerts negative feedback on the hypothalamus and pituitary gland → inhibits secretion of **GnRH** → decreases release of pituitary gonadotropins (**FSH** and **LH**), thereby suppressing estrus and ovulation in a dose-dependent manner.
ขนาดยาตามชนิดสัตว์
- To suppress estrus for synchronization · 1 mL per 110 pounds body weight (0.044 mg/kg) · PO · once daily · 15 consecutive days · May administer directly on tongue using a dose syringe or on the usual grain ration.
- For prevention of abortion/pregnancy loss · 0.088 mg/kg · PO · once daily
- To maintain pregnancy in mares with deficient progesterone levels · 0.044 mg/kg · PO · once daily · Until day 60, 120, or end of pregnancy · Three options: 1) until day 60+ AND endogenous progesterone >4 ng/mL; 2) until day 120; 3) until end of pregnancy.
- To maintain pregnancy in mares with placentitis · 22-44 mg (total dose; 10-20 mL) · PO · daily
- To suppress estrus (long-term) · 0.044 mg/kg · PO · daily
- For synchronization of estrous in sexually mature gilts that have had at least one estrous cycle · 6.8 mL (15 mg) per gilt · PO · once daily · 14 consecutive days · Apply as a top-dressing on a portion of gilt's daily feed allowance. Estrous should occur 4-9 days after completing treatment.
- Luteal insufficiency · 2 mL per 100 lbs of body weight · PO · once daily · Document luteal insufficiency and rule out infectious causes. Best to avoid during first trimester. Monitor pregnancy with ultrasound. Monitor carefully for pyometra.
- Luteal insufficiency, pre-term labor · 0.1 mL per 10 lb body weight · PO · once daily
วิธีการให้ยา
ข้อห้ามใช้
- Horses intended for food purposes
- Mares with chronic uterine infections
- Manufacturer lists pregnancy as a contraindication (though clinically used extensively to maintain pregnancy)
อาการไม่พึงประสงค์
- Minimal at labeled dosages
- Slight, sporadic elevations in Ca++, K+, alkaline phosphatase, and AST
- May exacerbate chronic uterine infections
- Risk of pyometra in dogs (due to exogenous progesterone effects)
อันตรกิริยาระหว่างยา
- Rifampin · May decrease progestin activity if administered concomitantly due to microsomal enzyme induction and increased progestin metabolism.
การติดตาม
- Pregnancy viability (via ultrasound)
- Endogenous progesterone levels (if treating luteal deficiency)
- Signs of pyometra in dogs
การได้รับยาเกินขนาด
The LD50 of altrenogest is 175-177 mg/kg in rats. No specific information is available regarding the effects of an accidental acute overdose in horses or other veterinary species.
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