Trilostane for Donkeys: Endocrine Uses, Dosing & 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 is a prescription medication that reduces the body's production of cortisol and other adrenal steroids. It works by inhibiting the enzyme 3-beta-hydroxysteroid dehydrogenase, which is involved in steroid hormone synthesis. In veterinary medicine, trilostane is FDA-approved for dogs with hyperadrenocorticism, but use in donkeys is extra-label and should be directed closely by your vet.

In donkeys, trilostane is not considered the usual first medication for pituitary pars intermedia dysfunction, also called PPID or equine Cushing's disease. Current equine and donkey references describe pergolide as the drug of choice for PPID, while trilostane may be considered in selected cases, especially when a donkey cannot tolerate pergolide or needs another management option.

Because donkeys have important endocrine differences from horses, including higher baseline ACTH values and a strong risk of hyperlipemia if appetite drops, medication choices need to be individualized. That makes monitoring especially important. Your vet may recommend repeat exams, body condition checks, and follow-up bloodwork to make sure treatment is helping without pushing cortisol too low.

In donkeys, trilostane is used mainly as an off-label endocrine medication for PPID. This condition is more common in older equids and can contribute to a long hair coat, delayed shedding, muscle loss, lethargy, increased drinking and urination, recurrent infections, and laminitis. A small equine study found improvement in signs such as lethargy, polyuria/polydipsia, and laminitis in horses treated with trilostane, but the evidence base is still much smaller than it is for pergolide.

That matters because trilostane is usually not the first-line choice. Donkey-focused continuing education materials and equine references continue to list pergolide as the preferred treatment for PPID, with trilostane reserved for selected situations. Your vet may discuss trilostane when pergolide causes appetite loss, when response to pergolide is incomplete, or when the diagnosis and treatment plan need a more tailored approach.

Trilostane does not cure PPID. Instead, it may help control some clinical signs by lowering adrenal steroid production. Donkeys with PPID often also need non-drug support, such as hoof care, diet changes, dental care, parasite control, and management of insulin dysregulation or laminitis if those problems are present.

There is no FDA-approved donkey label dose for trilostane, so dosing must be set by your vet. Published equine data describe once-daily oral dosing around 0.4 to 1 mg/kg, with one study reporting a mean dose of 0.5 mg/kg once daily in horses with equine Cushing's syndrome. In practice, your vet may start at the lower end and adjust based on response, appetite, body weight, and follow-up testing.

Trilostane is generally given by mouth with feed. Capsules should not be split or opened unless your vet specifically directs a compounded formulation. If a donkey needs a dose strength that is not commercially practical, your vet may discuss compounding, but consistency and pharmacy quality matter.

Monitoring is a major part of safe dosing. Your vet may recheck clinical signs, hydration, weight, hoof comfort, and bloodwork after starting treatment or changing the dose. Because donkeys are especially vulnerable to hyperlipemia when they go off feed, even mild appetite loss deserves prompt attention. If your donkey seems dull, stops eating, develops diarrhea, or looks weak after starting trilostane, contact your vet right away rather than waiting for the next scheduled recheck.

The most important concern with trilostane is lowering cortisol too much. In small animal references, this can lead to hypoadrenocorticism or an Addisonian crisis, which may cause lethargy, weakness, vomiting, diarrhea, collapse, shaking, or sudden worsening illness. Donkeys may not show the exact same pattern as dogs, but the same basic risk of excessive adrenal suppression is why close veterinary monitoring matters.

More common early side effects can include reduced appetite, dullness, lethargy, and digestive upset. Appetite changes deserve special attention in donkeys. Unlike many other species, donkeys can develop hyperlipemia quickly when they stop eating, and that complication can become life-threatening.

See your vet immediately if your donkey becomes weak, stops eating, has diarrhea, seems dehydrated, lies down more than usual, or shows signs of collapse. Also call promptly if drinking, urination, or laminitis signs suddenly worsen. Trilostane may need to be paused, adjusted, or replaced, but those decisions should be made with your vet based on the whole clinical picture.

Trilostane can interact with other medications that affect adrenal function, blood pressure, kidney perfusion, or potassium balance. Small animal references advise caution with ACE inhibitors such as enalapril or benazepril, potassium-sparing diuretics such as spironolactone, potassium supplements, ketoconazole, and mitotane. While some of these drugs are uncommon in donkeys, the interaction principles still matter.

Your vet should also know about any recent glucocorticoid use, because steroids can complicate endocrine testing and may affect how clinical signs are interpreted. In donkeys being evaluated for PPID, some drugs and stressful events can alter ACTH results, so timing of medication changes and blood sampling may be important.

Before starting trilostane, give your vet a full list of everything your donkey receives. That includes prescription drugs, pergolide, pain medications, ulcer medications, dewormers, supplements, and herbal products. If another medication is added later, ask whether it changes the monitoring plan or raises the risk of low cortisol, poor appetite, dehydration, or electrolyte problems.