Estriol Incurin in Dogs

Estriol, sold as Incurin, is a prescription medication used in dogs to help control estrogen-responsive urinary incontinence. It is labeled for ovariohysterectomized female dogs, meaning spayed females with urine leakage linked to reduced urethral tone after spay. This medication does not cure every cause of leaking urine, so your vet will usually want to rule out problems such as urinary tract infection, bladder stones, neurologic disease, excessive urine production, or an anatomic abnormality before deciding it is a good fit.

Incurin is one treatment option, not the only option. Many dogs with urethral sphincter mechanism incompetence improve with medication, and some need dose adjustments over time. In a masked field study summarized in the FDA label, 66% of treated dogs met treatment success criteria by day 14, compared with 37% of dogs given placebo. Some dogs stay controlled on lower maintenance doses after the starting period, which can help limit side effects and reduce monthly cost range.

Because estriol is a hormone, it should be used thoughtfully and under veterinary supervision. It is not considered appropriate for every dog with accidents in the house. If your dog is male, intact, pregnant, lactating, under 1 year old, or has another likely cause of incontinence, your vet may recommend a different workup or another medication instead.

See your vet immediately if your dog cannot pass urine, seems painful, is vomiting repeatedly, becomes weak, or has sudden behavior changes after starting any medication. Those signs can point to a more urgent urinary problem or a medication reaction that needs prompt attention.

Estriol is a natural estrogen. In spayed female dogs with hormone-responsive incontinence, lower estrogen activity can contribute to reduced resting tone of the urethra. Estriol helps increase urethral resting muscle tone, which can improve closure of the urethral sphincter and reduce urine leakage, especially when a dog is relaxed or sleeping.

The drug is absorbed after it is given by mouth and has a relatively short receptor occupancy time compared with some older estrogen therapies. That short action is one reason estriol is used instead of older estrogens in many dogs. The FDA label notes that estriol is rapidly absorbed, reaches peak blood levels within hours, and has an elimination half-life of about 8 to 12 hours in dogs, although enterohepatic recirculation can create multiple blood level peaks.

This medication works best when the main problem is urethral sphincter mechanism incompetence. If the real issue is a urinary tract infection, bladder inflammation, stones, spinal disease, congenital defect, or excessive urine production from another illness, estriol may not help enough on its own. That is why your vet may recommend urinalysis, urine culture, bloodwork, imaging, or blood pressure checks before or during treatment.

Some dogs respond to estriol alone, while others do better with a different medication such as phenylpropanolamine or with a combination plan. The right approach depends on your dog’s age, medical history, exam findings, and how well leakage improves after the first few weeks.

The most commonly reported side effects with Incurin are usually gastrointestinal or estrogen-related. In the FDA label, the more common reactions during the first 14 days included decreased appetite, vomiting, increased thirst, swollen vulva, anxiety, sexual attractiveness, sleepiness, hypersalivation, estrous behavior, and mammary enlargement. During later dose-adjustment phases, reported effects also included vulva licking, vulvovaginitis, lethargy, aggression, hyperactivity, cystitis, and local alopecia.

Many estrogenic side effects improve when the dose is lowered to the lowest effective amount. That is one reason your vet may start with the labeled induction dose and then taper down based on response. If your dog develops swollen mammary tissue, vulvar swelling, discharge, marked restlessness, or behavior changes, contact your vet promptly to discuss whether the dose should be adjusted or the medication stopped.

Serious complications appear uncommon at labeled doses, but estrogens as a class can affect bone marrow. The Incurin label states that some estrogens have been associated with bone marrow changes, and foreign post-market reports included anemia, leukopenia, and thrombocytopenia in one or more dogs. Merck also notes that estrogen exposure can be associated with bone marrow suppression. Because of that risk, your vet may recommend periodic bloodwork in some dogs, especially if treatment is long term or if your dog has other health concerns.

See your vet immediately if your dog becomes very weak, pale, collapses, has severe vomiting, stops eating, develops unusual bruising, or shows major aggression or neurologic changes. Those signs are not typical day-to-day effects and deserve urgent medical review.

Incurin is given by mouth and is not dosed by body weight. The FDA label describes a starting dose of 2 mg per dog once daily for 14 days. After that, your vet should reassess control of urine leakage and reduce to the lowest effective dose. In the field study, many dogs remained improved on lower maintenance schedules such as 1 mg once daily, 0.5 mg once daily, 1 mg every other day, or 0.5 mg every other day.

Give the medication exactly as your vet prescribes. It may be given with or without food. If your dog vomits on an empty stomach, ask your vet whether giving it with food is appropriate. Do not increase, decrease, or stop the dose on your own, because both underdosing and overdosing can create problems. Dose changes are usually spaced out so your vet can see how your dog responds before making another adjustment.

If you miss a dose, give it when you remember unless it is close to the next scheduled dose. In that case, skip the missed dose and return to the regular schedule. Do not double up. Tablets should be stored at or below 25 degrees C, or 77 degrees F, with brief excursions up to 40 degrees C, and kept in the blister pack until use.

People should handle this medication carefully. The label advises washing hands after administration, and VCA notes that pregnant women should not handle the medication unless necessary. If accidental human ingestion happens, contact a physician or Poison Control right away.

The clearest labeled interaction concern is with other estrogens. The Incurin label states that it should not be used with other estrogens, and the concomitant use with other estrogens has not been evaluated. Using multiple estrogen products together could increase the chance of hormone-related side effects without adding meaningful benefit.

The label also states that concomitant use with glucocorticoids has not been evaluated, and use in dogs with liver disease has not been evaluated. That does not always mean the combination is prohibited, but it does mean your vet should weigh risks and benefits carefully. Because estriol is processed through the liver, dogs with liver disease may need a more cautious plan or a different medication.

It is also important to think beyond direct drug interactions. Medications or diseases that increase thirst and urine production can make incontinence look worse even if urethral tone improves. Steroids, kidney disease, diabetes, Cushing's disease, and some seizure medications can all change how often a dog urinates. If your dog starts leaking more after a medication change, tell your vet about every prescription, supplement, and over-the-counter product your dog receives.

If your dog is taking phenylpropanolamine, thyroid medication, steroids, seizure medication, or hormone products, bring a full medication list to the appointment. Your vet can decide whether estriol alone, another medication, or a combination approach makes the most sense for your dog’s situation.