Trilostane (Vetoryl) for Dogs: Uses, Dosage & Side Effects

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Trilostane, sold under the brand name Vetoryl, is a prescription medication used to help manage hyperadrenocorticism, also called Cushing's disease, in dogs. It works by blocking an adrenal enzyme involved in making cortisol. That lowers cortisol production and can reduce many of the signs that make affected dogs feel unwell.

In the United States, Vetoryl is the FDA-approved oral medication labeled for both pituitary-dependent and adrenal-dependent Cushing's disease in dogs. It is a management tool, not a cure. If treatment is stopped, excess cortisol production can return and your dog's signs may come back.

Most dogs improve gradually over days to weeks. Pet parents often notice less thirst, less urination, less panting, and a more normal appetite and energy level once the dose is well matched to the dog. Because trilostane can also suppress adrenal function too much, regular follow-up with your vet is a key part of safe treatment.

Trilostane is used primarily to treat Cushing's disease in dogs. This condition happens when the body makes too much cortisol over time. The excess cortisol may come from a pituitary tumor signaling the adrenal glands too strongly, or from an adrenal tumor producing hormones more directly.

Dogs with Cushing's disease often drink and urinate more, pant more, seem hungrier than usual, develop a pot-bellied shape, lose hair, or have thin skin and repeated skin infections. Trilostane does not remove the underlying pituitary tumor, and it does not shrink an adrenal tumor. Instead, it helps control the hormone imbalance that causes the day-to-day symptoms.

Your vet may recommend trilostane when a dog's clinical signs and testing support Cushing's disease and when the family is ready for ongoing monitoring. In some adrenal tumor cases, surgery may also be discussed as another option. The best plan depends on the dog's overall health, test results, and the pet parent's goals and budget.

Trilostane dosing is individualized. The FDA label for Vetoryl lists a starting dose of 1-3 mg/lb (2.2-6.7 mg/kg) by mouth once daily, given with food. Your vet will usually start with the lowest practical capsule combination for your dog's body weight, then adjust based on how your dog feels and what follow-up lab work shows.

Recheck testing is a big part of dosing safely. The label recommends a recheck at about 10-14 days after starting or changing the dose, including a physical exam, chemistry panel with electrolytes, and an ACTH stimulation test performed 4-6 hours after dosing. Once a stable dose is found, dogs are typically rechecked at 30 days, 90 days, and then about every 3 months.

Some dogs do well on once-daily dosing. Others need twice-daily dosing if signs are not controlled for the full day. Do not split, open, or change capsules unless your vet specifically instructs you to do so. If you miss a dose, ask your vet how they want you to handle it. Never double up unless your vet tells you to.

The most common trilostane side effects in dogs are reduced appetite, vomiting, diarrhea, lethargy, and weakness. Mild stomach upset can happen early in treatment, but these signs should never be ignored because they can also signal that cortisol has dropped too low.

The most important serious risk is hypoadrenocorticism, sometimes called an Addisonian crisis. This can happen at any dose and may develop suddenly. Warning signs include repeated vomiting, diarrhea, marked tiredness, shaking, weakness, collapse, or a dramatic drop in appetite or water intake. See your vet immediately if these signs appear, and stop the medication until your vet advises otherwise.

Rare but severe complications reported with trilostane include major electrolyte changes, kidney-related abnormalities, adrenal necrosis or rupture, hemorrhagic diarrhea, and death. That sounds alarming, but careful monitoring helps lower risk. If your dog seems "off" after starting trilostane, trust your instincts and contact your vet promptly.

Trilostane can interact with other medications that affect aldosterone, potassium balance, blood pressure, or adrenal function. The FDA label and veterinary references advise caution with ACE inhibitors such as enalapril or benazepril because the combination may increase the risk of low aldosterone effects, electrolyte problems, reduced blood volume, and decreased kidney perfusion.

Potassium-sparing diuretics, especially spironolactone, are a bigger concern and generally should not be used with trilostane because both drugs can push potassium too high. Potassium supplements may also increase risk. Other medications commonly listed for caution include ketoconazole and mitotane, since they can also affect adrenal hormone production.

Before your dog starts trilostane, give your vet a full list of everything your dog takes. That includes prescription drugs, heart medications, supplements, probiotics, and over-the-counter products. This is especially important for dogs with kidney disease, liver disease, or complex medical problems, because those dogs may need a different plan.