Aglepristone
Aglepristone is a synthetic steroid acting as a **progesterone receptor antagonist**. It is primarily used in veterinary medicine for **pregnancy termination** in dogs and cats, as well as the medical management of **pyometra** and feline **fibroadenomatous mammary hyperplasia**. Because it is formulated in an oil-alcohol base, localized injection site reactions are common. **Clinical Pearl**: As a competitive antagonist, aglepristone does not decrease circulating endogenous progesterone levels; rather, it blocks progesterone's biological action directly at the receptor level.
Mecanismo: Aglepristone competitively binds to **progesterone (P4) receptors** in the uterus and other target tissues. * In dogs, its affinity for uterine progesterone receptors is ~3x that of endogenous progesterone; in queens, it is ~9x greater. * **Pathway**: Aglepristone binding → blockade of progesterone signaling → withdrawal of pregnancy support → cervical dilation and resumption of myometrial contractility → fetal resorption or abortion (usually within 7 days). * It also binds to **glucocorticoid receptors** acting as an antagonist, which can block endogenous or exogenously administered glucocorticoids from acting at these sites.
Dosificación por especie
- To terminate pregnancy (up to day 45) · 10 mg/kg (0.33 mL/kg) subcutaneous injection only. Repeat one time, 24 hours after the first injection. · SC · q24h · 2 doses · A maximum of 5 mL should be injected at any one site. Light massage of the injection site is recommended.
- To induce parturition · At day 60 (post-estimated LH surge): 15 mg/kg SC and another dose 24 hours later. Subsequently, give oxytocin 0.15 Units/kg SC at hourly intervals until last pup is delivered. · SC · q24h · 2 doses · Additional studies confirming efficacy and safety are warranted before routine clinical application.
- To induce parturition · On or after day 58 of pregnancy: 15 mg/kg subcutaneously; repeat in 9 hours. · SC · Repeat in 9 hours · 2 doses · Expulsion of first pup occurred between 32 and 56 hours after treatment. Use standard protocols to assist with birth.
- As an adjunct to treating pyometra/metritis (preserve fertility) · Treatment begun at week 2-4 of diestrus with a single SC injection of aglepristone at 10 mg/kg. Doses are repeated at days 2, 7, and 14. · SC · Days 1, 2, 7, 14 · 14 days · During first 7 days, daily injections of amoxicillin/clavulanic acid were also given.
- For closed cervix pyometra · 6 mg/kg twice daily on the first day followed by the same dose once daily on days 2, 3, and 4. Some prefer using larger doses (10mg/kg) once daily on days 1, 3, and 8, then follow up also on days 15 and 28 depending on the bitch's condition. · SC · Variable · Variable
- For metritis · 10 mg/kg subcutaneously once daily on days 1, 2 and 8. · SC · Days 1, 2, 8 · 8 days
- For open or closed pyometra · aglepristone 10 mg/kg subcutaneously once daily on days 1, 2 and 8 and cloprostenol 1 microgram/kg subcutaneously on days 3 to 7. · SC · Days 1, 2, 8 · 8 days · Bitches with closed pyometra or with elevated temperature/dehydration should also receive IV fluids and antibiotics. If unresolved, additional doses on days 14 and 28.
Vías de administración
Contraindicaciones
- Known hypersensitivity to aglepristone
- Pregnancy (unless used specifically for pregnancy termination or inducing parturition)
- Hypoadrenocorticism (Addison's disease) or genetic predisposition to it
- Peritonitis (must be ruled out before using for pyometra)
- Caution in patients with poor health, diabetes, or impaired hepatic/renal function
Efectos adversos
- Injection site reactions (pain, edema, skin thickening, ulceration, localized lymph node enlargement)
- Anorexia (25%)
- Excitation (23%)
- Depression (21%)
- Diarrhea (13%)
- Uterine infections (3.4%)
- Vomiting (2%)
- Brown mucoid vaginal discharge (associated with pregnancy termination)
- Mammary gland congestion
Interacciones farmacológicas
- Progestins (natural or synthetic) · Could reduce the efficacy of aglepristone
- Glucocorticoids · Aglepristone could reduce the efficacy of glucocorticoid treatment due to receptor antagonism · moderate
- Ketoconazole · May interact with aglepristone (manufacturer warning, likely due to CYP450 enzyme inhibition)
- Itraconazole · May interact with aglepristone (manufacturer warning)
- Erythromycin · May interact with aglepristone (manufacturer warning)
Monitoreo
- Clinical efficacy
- For pregnancy termination: ultrasound 10 days after treatment and at least 30 days after mating
- Injection site reactions (pain, swelling, ulceration)
- Systemic adverse effects (anorexia, excitation, depression, diarrhea)
Sobredosis
When administered at 3X (30 mg/kg) recommended doses, bitches demonstrated no untoward systemic effects. Localized reactions were noted at the injection site, presumably due to the larger volumes injected.
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