What Is Alizin and What Is It Used For?
Alizin is the brand name for aglepristone, an injectable prescription medication used in dogs primarily to terminate an unwanted pregnancy following an accidental or unplanned mating (a “mismating”). It is widely licensed for veterinary use, particularly in the UK, Europe and many other countries.
Aglepristone is a progesterone antagonist (also called an antiprogestin). Pregnancy in dogs depends on the hormone progesterone, which maintains the uterine lining and supports the developing litter. Aglepristone works by blocking progesterone receptors — it occupies the receptors without activating them, so the body’s own progesterone can no longer act. Without progesterone support, the pregnancy cannot continue.
The two main veterinary uses of Alizin are:
- Pregnancy termination after a mismating — its principal, licensed use. It can be used up to day 45 after the mating.
- Pyometra management — in carefully selected cases, aglepristone may be used as part of the medical management of pyometra (a serious infection of the uterus), generally alongside antibiotics and supportive care.
A few things are essential to understand. Alizin is an injectable, prescription-only medicine that is administered by a veterinarian — it is not something given at home. The decision to use it, and the confirmation of how far along any pregnancy is, require a veterinary examination. And aglepristone does not prevent future seasons or future pregnancies — so it is a treatment for one specific situation, not a long-term contraceptive. For more, see PuppaDogs’ guide to Alizin for dogs.
How the Alizin Dosage Calculator Works
Alizin dosing is based purely on body weight. The calculator:
- Applies the standard 10 mg/kg dose.
- Converts that into the volume to inject from the 30 mg/mL solution.
- Shows the injection schedule for the chosen use.
- Flags health conditions that need veterinary caution.
Enter your dog’s weight, choose the reason for use, tick any health considerations, then press Calculate Dose. Remember that the injection itself is given by your veterinarian.
How Alizin Doses Are Calculated for Dogs
The Standard Dose and Schedule
The standard dose of Alizin (aglepristone) for dogs is:
10 mg/kg of body weight, by subcutaneous injection.
Alizin is supplied as a 30 mg/mL solution, so the volume works out to 0.33 mL per kilogram of body weight.
For pregnancy termination, the treatment is two injections given 24 hours apart — one on day 1 and one on day 2. For pyometra management, a longer schedule is used, typically injections on days 1, 2 and 8 (and sometimes day 15), as directed by the veterinarian.
If the calculated volume is larger than 5 mL, the product information advises splitting the dose between two separate injection sites.
Timing Matters
For a mismating, Alizin is effective when given up to day 45 of the pregnancy. It works at any stage within that window, but the earlier it is given, the higher the success rate and the gentler the process tends to be. This is one reason a prompt veterinary visit after a known or suspected mismating is important.
Alizin Dosage Chart for Dogs
This chart shows the per-injection dose and volume. It is a reference only — the injection is given by your veterinarian.
| Dog weight | Dose (10 mg/kg) | Volume (30 mg/mL) |
|---|---|---|
| 5 kg (11 lb) | 50 mg | ~1.7 mL |
| 10 kg (22 lb) | 100 mg | ~3.3 mL |
| 20 kg (44 lb) | 200 mg | ~6.7 mL |
| 30 kg (66 lb) | 300 mg | ~10 mL |
| 40 kg (88 lb) | 400 mg | ~13.3 mL |
For pregnancy termination, each amount above is given twice — on day 1 and again on day 2.
How Alizin Is Given and What to Expect
Alizin is administered by your veterinarian as a subcutaneous injection, usually at the scruff of the neck. Before treatment, your vet will confirm the situation — examining your dog and, where appropriate, using ultrasound or blood tests to assess the pregnancy.
After treatment:
- It is normal to see a vaginal discharge and some physical changes over the following days as the body responds.
- For an early termination, the process is generally complete within about a week to ten days; given later in pregnancy, the visible process can be more noticeable.
- Your veterinarian will usually arrange a follow-up examination or ultrasound (often around 10 days to a few weeks later) to confirm the treatment has worked, because occasionally a repeat treatment is needed.
Contact your veterinarian promptly if your dog becomes unwell, develops a fever, has heavy or prolonged bleeding, seems to be in pain, or is not eating.
Side Effects and Safety
Aglepristone is generally well tolerated. The most common effects are local — temporary swelling, discomfort or a small reaction at the injection site — and the expected reproductive effects of the treatment, such as vaginal discharge. Some dogs are a little subdued for a day or two.
Aglepristone should be used with caution, or avoided, in dogs with:
- Significant liver or kidney disease
- A known hypersensitivity to aglepristone
- Diabetes — the timing should be discussed with the vet
Your veterinarian will take a full history and decide whether Alizin is appropriate for your individual dog.
Important Things to Know
- It is not a long-term contraceptive. Aglepristone treats a single mismating; your dog will continue to have seasons and can become pregnant again. If you do not intend to breed, discuss spaying with your veterinarian as the permanent solution.
- A mismating is time-sensitive. Because earlier treatment works better, contact your veterinarian as soon as you know or suspect an unplanned mating, rather than waiting.
- Pyometra is an emergency. If aglepristone is being considered for pyometra, that is a serious illness requiring urgent, comprehensive veterinary care — medical management with aglepristone is only suitable for some cases, and surgery is often still the safest choice.
Conclusion
Alizin (aglepristone) is an effective, veterinary-administered treatment for terminating an unwanted canine pregnancy after a mismating, dosed simply at 10 mg/kg (0.33 mL/kg of the 30 mg/mL solution) by subcutaneous injection, repeated 24 hours later. The calculator above estimates the dose and volume so you can understand the treatment. But every part of the process — confirming the pregnancy stage, giving the injections, and checking the outcome — belongs with your veterinarian. If an unplanned mating has occurred, contact your vet promptly, and discuss spaying as the long-term answer.
Frequently Asked Questions
What is the dose of Alizin for dogs?
The standard dose of Alizin (aglepristone) for dogs is 10 mg/kg of body weight, given by subcutaneous injection. Because Alizin is a 30 mg/mL solution, that is 0.33 mL per kilogram. For pregnancy termination it is given as two injections 24 hours apart. The injection is administered by a veterinarian.
How late in pregnancy can Alizin be used?
Alizin can be used to terminate a pregnancy up to day 45 after the mating. It is effective throughout that window, but the earlier it is given, the higher the success rate and the gentler the process. A prompt veterinary visit after a known or suspected mismating is therefore important.
How is Alizin given to a dog?
Alizin is given by a veterinarian as a subcutaneous injection, usually at the scruff of the neck. It is not a home medication. For pregnancy termination the schedule is two injections 24 hours apart; for pyometra management a longer schedule such as days 1, 2 and 8 is used.
What should I expect after my dog is treated with Alizin?
It is normal to see a vaginal discharge and some physical changes over the following days. An early termination is usually complete within about a week to ten days. Your vet will arrange a follow-up examination or ultrasound to confirm the treatment worked, as occasionally a repeat dose is needed. Contact your vet if your dog seems unwell.
Does Alizin stop my dog getting pregnant again?
No. Aglepristone treats one specific mismating – it does not prevent future seasons or future pregnancies, and your dog can become pregnant again. If you do not intend to breed from your dog, discuss spaying with your veterinarian as the permanent solution.
Is Alizin safe for dogs?
Aglepristone is generally well tolerated, with side effects usually limited to a temporary injection-site reaction and the expected reproductive effects. It should be used with caution or avoided in dogs with significant liver or kidney disease, diabetes, or a known hypersensitivity. A veterinarian assesses each dog before treatment.
Related PuppaDogs Calculators
Continue building your dog’s personalised care plan with these related PuppaDogs calculators:
- Dog Pregnancy / Whelping Due-Date Calculator
- Puppy Weight Predictor (Adult Weight Calculator)
- Heatstroke Risk Calculator for Dogs
- Bloat (GDV) Risk Calculator for Dogs
- Dog Life Expectancy Calculator (Breed, Body Condition, Lifestyle)
- Spay/Neuter Timing Calculator for Dogs (Breed-Specific)
References & Further Reading
The dosing ranges and safety information on this page are drawn from the following veterinary references. Always defer to your own veterinarian and the manufacturer’s label for your specific product.
- Alizin (aglepristone) – Summary of Product Characteristics, Virbac; UK Veterinary Medicines Directorate Product Information Database.
- Plumb DC. Plumb’s Veterinary Drug Handbook. 10th ed. Hoboken, NJ: Wiley-Blackwell, 2023 – aglepristone monograph.
- Merck Veterinary Manual. Mismating and pregnancy termination in dogs; pyometra. merckvetmanual.com.
- Fieni F, et al. Clinical use of aglepristone in the bitch and queen. World Small Animal Veterinary Association (WSAVA) Congress proceedings.
- PuppaDogs. Alizin for Dogs: Safe Pregnancy Termination. puppadogs.com.
