Aglepristone
RU-534
Also known as: Alizine · RU-534 · RU46534 · RU-46534
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| 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 | 🌎 NA |
| 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 | 🌎 NA |
| 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 | 🌎 NA |
| 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 | 🌎 NA |
| 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 | 🌎 NA |
| For metritis | 10 mg/kg subcutaneously once daily on days 1, 2 and 8. | SC | Days 1, 2, 8 | 8 days | 🌎 NA |
| 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 | 🌎 NA |
| For pyometra | 10 mg/kg SC on days 1, 2, 8, 15, & 29. Give misoprostol 10 micrograms/kg PO twice daily on days 3 through 12. | SC | Days 1, 2, 8, 15, 29 | 29 days | 🌎 NA |
| Pregnancy termination | 10 mg/kg | SC | q24h | 2 doses | 🌍 EU |
| Progesterone-induced acromegaly | 10 mg/kg | SC | q24h for 2 doses, then q7d | 5 doses total | 🌍 EU |
| Pyometra | 10 mg/kg | SC | Days 1, 2, and 7 | 3 doses (up to 5) | 🌍 EU |
- To terminate pregnancy (up to day 45): A maximum of 5 mL should be injected at any one site. Light massage of the injection site is recommended.
- To induce parturition: Additional studies confirming efficacy and safety are warranted before routine clinical application.
- To induce parturition: 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): During first 7 days, daily injections of amoxicillin/clavulanic acid were also given.
- For open or closed pyometra: 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.
- For pyometra: Approximately 75% of cases show significant clinical improvement without developing adverse effects associated with prostaglandins.
- Pregnancy termination: Maximum of 5 ml injected at any one site.
- Progesterone-induced acromegaly: Maximum of 5 ml injected at any one site.
- Pyometra: Maximum of 5 ml injected at any one site. Additional doses may be given on days 14 and 21 if there is an inadequate response.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For treating mammary fibroadenomatous hyperplasia | 20 mg/kg aglepristone subcutaneously once weekly until resolution of signs. | SC | q7d | Until resolution | 🌎 NA |
| For treating mammary fibroadenomatous hyperplasia | 10 mg/kg SC on two consecutive days, once weekly. | SC | Two consecutive days weekly | 3-5 weeks | 🌎 NA |
| To terminate pregnancy (up to day 45) | 15 mg/kg SC twice 24 hours apart. | SC | q24h | 2 doses | 🌎 NA |
| Pregnancy termination | 15 mg/kg | SC | q24h | 2 doses | 🌍 EU |
| Fibroadenomatous hyperplasia | 20 mg/kg | SC | q7d | Until resolution | 🌍 EU |
| Pyometra | 15 mg/kg | SC | Days 1, 2, and 7 | 3 doses (up to 5) | 🌍 EU |
- For treating mammary fibroadenomatous hyperplasia: Cats with HR > 200 BPM should receive atenolol at 6.25 mg (total dose) until HR < 200 BPM with regression in mammary gland size.
- For treating mammary fibroadenomatous hyperplasia: Complete regression occurs on average 3-4 weeks. Relapses can occur, particularly if treated with long-acting progestins; these cats should be treated for 5 weeks.
- To terminate pregnancy (up to day 45): Efficacy is 95% if administered before implantation, 85% if after implantation. Termination occurs within 3 days in 50% of queens.
- Pregnancy termination: Maximum of 5 ml injected at any one site.
- Fibroadenomatous hyperplasia: Maximum of 5 ml injected at any one site. Consider atenolol if cat is tachycardic with heart rate >200 bpm.
- Pyometra: Maximum of 5 ml injected at any one site. Additional doses may be given on days 14 and 21 if there is an inadequate response.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
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.
Mechanism of action
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.
Safety & warnings
Contraindications
- 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
Adverse effects
- 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
Precautions
WARNING: Accidental injection of this product can induce abortion; it should not be administered or handled by pregnant women. Accidental injection can also cause severe pain, intense swelling, and ischemic necrosis that can lead to serious sequelae, including loss of a digit. Seek prompt medical attention if accidentally injected.
- Injection Site Care: Light massage of the injection site is recommended after administration. Larger dogs should not receive more than 5 mL at any one SC injection site. Administering into the scruff of the neck may help avoid severe injection reactions.
- Pyometra: When used for pyometra, there is a substantial risk of treatment failure, and ovariohysterectomy may ultimately be required.
Drug interactions
Could reduce the efficacy of aglepristone
Aglepristone could reduce the efficacy of glucocorticoid treatment due to receptor antagonism
May interact with aglepristone (manufacturer warning, likely due to CYP450 enzyme inhibition)
May interact with aglepristone (manufacturer warning)
May interact with aglepristone (manufacturer warning)
Monitoring
- 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)
Pharmacokinetics
Half-life
Absorption
In dogs, after injecting two doses of 10 mg/kg 24 hours apart, peak serum levels occur about 2.5 days later.
Distribution
Highly lipophilic, distributes widely into tissues.
Metabolism
Hepatic metabolism is likely, given potential interactions with CYP450 inhibitors like ketoconazole.
Elimination
The majority (90%) of the drug is excreted via the feces.
Overdose
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.
Available products
Formulations
- Injectable solution (30 mg/mL)
Veterinary
- Aglepristone 30 mg/mL in 5 mL & 10 mL vials (Alizine® or Alizin®)
Regulatory status
Authorized in multiple EU member states.
POM-V classification.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Aglepristone injection should be stored below 25°C and protected from light. The manufacturer recommends using the product within 28 days of withdrawing the first dose. Due to the product's oil/alcohol vehicle formulation, it should not be mixed with any other medication.
Client information
- Veterinary Administration Only: Only veterinary professionals should handle and administer this product due to severe risks associated with accidental human injection.
- Pregnancy Termination: When used for pregnancy termination in the bitch, understand that aglepristone might only be 95% effective when used between days 26-45.
- Vaginal Discharge: A brown mucoid vaginal discharge can be seen approximately 24 hours before fetal expulsion.
- Side Effects: Your pet may exhibit lack of appetite, excitement, restlessness or depression, vomiting, or diarrhea after treatment.
- When to Call the Vet: Contact your veterinarian if your pet exhibits a purulent (pus-like) or hemorrhagic (bloody) discharge after treatment, or if vaginal discharge persists 3 weeks after treatment.
- Pyometra Treatment: When used for pyometra, there is a substantial risk of treatment failure, and surgical removal of the uterus and ovaries (spay) may ultimately be required.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.