Trilostane (Vetoryl) for Cushing’s Treatment: What You Must Know

WeightQ&AMeongsiljang Veterinary Advisory Board

We’ve compiled everything pet owners need to know about trilostane (Vetoryl), a treatment for canine Cushing’s syndrome, including how it works, how to administer it, potential side effects, and the monitoring tests required.

What is Trilostane (Vetoryl)?

An elderly dog receiving veterinary care

Trilostane (brand name Vetoryl) is the most widely used oral medication for treating Cushing’s disease (hyperadrenocorticism) in dogs. It works by blocking the adrenal glands’ overproduction of cortisol, which helps alleviate symptoms such as excessive drinking and urination, as well as changes to the abdomen and skin. The most critical point is that you must never adjust the dosage on your own. Your veterinarian will determine and adjust the dose based on ACTH stimulation test results; stopping or changing the dose without professional guidance can lead to acute adrenal insufficiency, a life-threatening emergency.

Why Does Cushing’s Syndrome Occur, and Why Is Trilostane Used?

About 85% of Cushing’s disease cases are caused by a small tumor in the pituitary gland, located at the base of the brain, which overstimulates the adrenal glands. The remaining cases result from tumors directly on the adrenal glands themselves. In both scenarios, the end result is excessively high cortisol levels in the blood, leading to symptoms such as excessive thirst, a distended abdomen, and symmetrical hair loss. Trilostane works by directly inhibiting 3β-HSD, the enzyme responsible for cortisol production, making it effective regardless of whether the cause is pituitary or adrenal. Therefore, it is used as a first-line treatment.

Key Signs of Cushing’s Syndrome in Dogs

If several of the following signs appear together, consider testing for Cushing’s disease. When trilostane therapy is effective, most pets show a reduction in water intake and urine output within the first month. - Polydipsia and polyuria: Drinking significantly more water than usual, with a noticeable increase in urine volume - Abdominal distension: A pendulous, “pot-bellied” appearance - Symmetrical alopecia: Hair loss occurring symmetrically on the flanks and trunk - Skin changes: Thinning skin, poor wound healing, and occasionally calcinosis cutis (calcium deposits in the skin) - Muscle weakness: Difficulty with stairs or walks, accompanied by panting - Polyphagia: Increased appetite, seeking food much more than usual

An elderly dog with a distended abdomen and hair loss

Trilostane vs Mitotane Comparison

Item	Trilostane (Vetoryl)	Mitotane (Lysodren)
Mechanism of action	Blocks cortisol-synthesizing enzyme (reversible)	Destroys adrenal cortex cells (irreversible)
Administration frequency	Once or twice daily with food	Daily during induction → once or twice weekly during maintenance
Regular testing	ACTH stimulation test 2–4 hours after dosing	At the end of induction and periodically thereafter
Typical side effects	Decreased appetite, vomiting, lethargy, acute adrenal insufficiency	Vomiting, diarrhea, neurological signs, permanent adrenal insufficiency
Current prescribing trend	First-line choice in most countries	Declining, used as an adjunct or alternative option

Compiled based on the BSAVA Manual of Dermatology and veterinary internal medicine textbooks

Administration — With Food, at Consistent Times

Veterinary pharmacology textbooks and the study by Perez-Alenza et al. (2017) recommend an initial dose of 0.5–1 mg per kilogram of body weight, administered once or twice daily. However, the exact dosage must be determined by your veterinarian based on your pet’s weight, test results, and clinical signs. Here are three key points for pet owners to keep in mind: - Administer with food: Giving the medication on an empty stomach can lead to inconsistent absorption. - Maintain a consistent schedule: Since ACTH stimulation tests are performed 2–4 hours after administration, please note the timing carefully. - Do not crush the capsule: If the powder comes into contact with human skin, it may affect hormone levels.

Administering medication along with food

Contact Your Vet Immediately If You Notice These Symptoms

Trilostane is highly effective, but in rare cases, cortisol levels can drop too low, leading to acute adrenal insufficiency. If you notice any of the following signs, stop the medication immediately and contact your veterinarian on the same day: - Sudden, complete loss of appetite - Repeated vomiting and diarrhea - Extreme lethargy or staggering, as if about to collapse - A noticeably lower body temperature than usual and pale gums - Neurological symptoms such as tremors or seizures Do not decide on your own when to restart the medication; always follow your veterinarian’s instructions.

Monitoring — ACTH Stimulation Test Schedule

Trilostane isn’t a “give and forget” medication; it requires regular monitoring to fine-tune the dosage. According to standard veterinary internal medicine guidelines, the recommended schedule is as follows: - 10–15 days after starting treatment: Perform the first ACTH stimulation test to confirm response. - 1 month and 3 months later: Reassess whether the dosage is appropriate. - Every 3–6 months thereafter: Conduct long-term maintenance monitoring. - If symptoms recur or worsen: Test immediately, regardless of the scheduled timeline. Tests should be performed 2–4 hours after administering the medication, and the dosage will be finely adjusted within the 0.5–1 mg/kg range based on the results.

Things to Keep in Mind for Home Care

Weight management and diet are part of the treatment. Dogs with Cushing’s disease tend to lose muscle mass and gain fat, which can strain their joints and heart. A high-protein, moderate-fat diet is recommended, and it’s important to maintain the weight range approved by your veterinarian. If you’re unsure about ingredient choices for weakened joints, check out our Dog Joint Supplement Ingredient Guide. Keeping a simple daily record of water intake, urination frequency, and appetite helps your veterinarian determine the right time to adjust dosages more accurately.

Daily care log and water bowl for your dog

If an Adrenal Tumor Is Confirmed

Trilostane plays a vital role even when the tumor is located directly in the adrenal gland. According to the BSAVA Manual of Canine and Feline Dermatology, trilostane is the drug of choice to stabilize patients before surgery (adrenalectomy) and to reduce postoperative complications. In cases where surgery is not feasible or the tumor is too advanced, long-term management with medication alone may be pursued. Therefore, imaging tests are essential at the diagnostic stage to distinguish between pituitary-dependent and adrenal-dependent causes.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Does trilostane need to be given for life?

Pituitary-dependent Cushing’s disease usually requires lifelong medication because the underlying cause remains. In contrast, adrenal tumors can often be cured with surgery, allowing the medication to be discontinued, although it is still necessary for a certain period before and after the procedure.

I forgot to give my pet their medication. Can I give them two doses at once?

Absolutely not. Double-dosing significantly increases the risk of acute adrenal insufficiency. Skip the missed dose and administer the regular amount at the next scheduled time.

Is it okay for people to handle the medication?

If the capsule remains intact, there’s no major concern, but pregnant or breastfeeding individuals should avoid skin contact. It’s safest not to break or open the capsule.

Does drinking less water mean the medication will work better?

That's right. Typically, water intake and urine output decrease first within a month. However, if these drop too rapidly or if your pet loses its appetite, it could be a sign of an overdose, so consult your veterinarian.

Can my pet take this if they have other underlying health conditions?

If your pet has kidney disease, liver disease, or heart disease, the dosage should be adjusted more conservatively. Please inform your veterinarian about all medications and supplements your pet is currently taking.

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References

[1] Warman S., '74 The dog with hyperadrenocorticism', 100 Top Consultations in Small Animal General Practice

[2] BSAVA Manual of Canine and Feline Dermatology, 4th Ed — Hyperadrenocorticism, Trilostane therapy

[3] Clinical Medicine of the Dog and Cat, 4th Ed — Trilostane Therapy for hyperadrenocorticism

[4] Perez-Alenza D., 2017 — Trilostane dosing recommendations in canine hyperadrenocorticism