Trilostane is a prescription medication marketed under the brand name Vetoryl (manufactured by Dechra Veterinary Products) and is FDA-approved for the treatment of hyperadrenocorticism (Cushing’s disease) in dogs. It works by competitively inhibiting the enzyme 3-beta-hydroxysteroid dehydrogenase in the adrenal glands, which reduces the production of cortisol and other adrenal steroids. Cushing’s disease is a common endocrine disorder in middle-aged to older dogs, most frequently caused by a pituitary gland tumor (pituitary-dependent, approximately 80-85% of cases) or an adrenal gland tumor (adrenal-dependent, approximately 15-20% of cases). Trilostane has largely replaced mitotane (Lysodren) as the first-line medical treatment for canine Cushing’s disease due to its more predictable safety profile.
What Is Trilostane Used For?
Veterinarians prescribe trilostane for:
- Pituitary-dependent hyperadrenocorticism (PDH): The most common form of Cushing’s disease, caused by an ACTH-secreting pituitary tumor
- Adrenal-dependent hyperadrenocorticism (ADH): Caused by a cortisol-secreting adrenal tumor, when surgery is not an option or as preoperative stabilization
Common signs of Cushing’s disease that trilostane helps control include excessive thirst and urination, increased appetite, pot-bellied appearance, hair loss, skin thinning, muscle weakness, panting, and recurrent infections. Consult your veterinarian for proper diagnosis, which typically requires ACTH stimulation testing, low-dose dexamethasone suppression testing, and abdominal imaging.
Dosage
The recommended starting dose of trilostane is approximately 1 to 2 mg/kg orally once daily, given with food. Some dogs require twice-daily dosing. Your veterinarian will titrate the dose based on ACTH stimulation test results and clinical response.
| Dog’s Weight | Starting Dose Range | Common Capsule Sizes |
|---|---|---|
| Under 11 lbs (5 kg) | 5-10 mg once daily | 5 mg, 10 mg |
| 11-22 lbs (5-10 kg) | 10-20 mg once daily | 10 mg, 30 mg |
| 22-44 lbs (10-20 kg) | 30-40 mg once daily | 30 mg |
| 44-66 lbs (20-30 kg) | 30-60 mg once daily | 30 mg, 60 mg |
| 66-88 lbs (30-40 kg) | 60 mg once daily | 60 mg |
| Over 88 lbs (40 kg) | 60-120 mg once daily | 60 mg, 120 mg |
Vetoryl capsules are available in 5 mg, 10 mg, 30 mg, 60 mg, and 120 mg strengths. Always give with food to improve absorption. Do not open or split capsules. An ACTH stimulation test should be performed at 10 days, 4 weeks, and 12 weeks after starting therapy, and then every 3 months or as directed. Your veterinarian will adjust the dose based on results.
Side Effects
| Common Side Effects | Serious Side Effects (Contact Your Vet Immediately) |
|---|---|
| Decreased appetite | Signs of adrenal insufficiency (weakness, collapse, vomiting, diarrhea, shaking) |
| Mild lethargy | Severe vomiting or bloody diarrhea |
| Mild diarrhea or soft stool | Sudden profound weakness or collapse |
| Electrolyte abnormalities (hyperkalemia, hyponatremia) | |
| Adrenal necrosis (rare but potentially fatal) |
Adrenal insufficiency (Addisonian crisis) is the most serious potential complication of trilostane therapy and constitutes a veterinary emergency. Signs include severe lethargy, weakness, vomiting, diarrhea, collapse, and shock. If you observe these signs, stop trilostane immediately and contact your veterinarian or emergency clinic. Keep prednisone on hand as directed by your veterinarian for emergency use.
Drug Interactions
- ACE inhibitors (enalapril, benazepril): Use with caution; may increase risk of hyperkalemia.
- Potassium-sparing diuretics (spironolactone): May increase risk of hyperkalemia.
- Ketoconazole and other azole antifungals: May affect adrenal steroid synthesis.
- Mitotane (Lysodren): Do not use concurrently; both suppress adrenal function.
- Insulin: Cushing’s treatment may alter insulin requirements in diabetic dogs; monitor closely.
Always inform your veterinarian of all medications and supplements your dog is taking.
Contraindications
Trilostane should not be used in:
- Pregnant or lactating dogs (may cause abortion or fetal abnormalities)
- Dogs with primary hepatic disease or renal insufficiency (use with extreme caution)
- Dogs with known hypersensitivity to trilostane
- Dogs weighing less than 4.4 lbs (2 kg) (insufficient safety data)
Use with caution in dogs with pre-existing heart disease or concurrent diabetes mellitus, as cortisol reduction may affect cardiac function and insulin sensitivity. Your veterinarian will evaluate your dog thoroughly before initiating trilostane.
Storage
- Store at controlled room temperature, 68-77 degrees F (20-25 degrees C).
- Keep in original packaging.
- Protect from moisture and light.
- Trilostane may be absorbed through the skin; wash hands after handling capsules, especially if pregnant (trilostane may affect human fetal development).
- Keep out of reach of children and pets.
Frequently Asked Questions
How long does trilostane take to work? Many owners notice improvement in water intake, urination, and appetite within 2 to 4 weeks. Full resolution of skin and coat changes may take 3 to 6 months. ACTH stimulation tests at scheduled intervals guide dose optimization. Consult your veterinarian.
Is trilostane a cure for Cushing’s disease? No. Trilostane controls cortisol production but does not eliminate the underlying pituitary or adrenal tumor. It is a lifelong management therapy. Surgery (adrenalectomy or hypophysectomy at specialized centers) may be curative in select cases; discuss options with your veterinarian.
Why does my dog need ACTH stimulation tests so frequently? ACTH stimulation tests measure your dog’s cortisol response and are essential for ensuring the trilostane dose provides adequate cortisol suppression without causing dangerous adrenal insufficiency. Both overdosing and underdosing have significant health consequences.
What should I do if my dog seems sick on trilostane? Stop trilostane and contact your veterinarian immediately. Signs of adrenal insufficiency (weakness, collapse, vomiting, severe lethargy) require urgent veterinary care. Your veterinarian may instruct you to give an emergency dose of prednisone while transporting your dog to the clinic.
Is trilostane safe for people to handle? Trilostane can be absorbed through the skin and may affect human steroid hormone production. Always wash hands thoroughly after handling capsules. Pregnant women should avoid handling trilostane entirely.
This content is for informational purposes only and is not a substitute for professional veterinary advice. Always consult your veterinarian before starting, changing, or stopping any medication for your dog.