# Trilostane: veterinary dose and monograph

> Trilostane is a veterinary drug. Reversible inhibitor of 3-β-hydroxysteroid dehydrogenase — blocks adrenal cortisol synthesis and is the medical treatment of choice for canine hyperadrenocorticism (Cushing’s disease), both pituitary- and adrenal-dependent. Indications include canine pituitary-dependent hyperadrenocorticism; canine adrenal-dependent hyperadrenocorticism; feline hyperadrenocorticism (off-label). This monograph lists 4 reference doses for dogs, cats and horses, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/trilostane · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Veterinary drug
- **Also known as:** Vetoryl
- **Species with doses:** Dogs, Cats and Horses
- **General dose range:** 1–3 mg/kg PO q24h (or divided q12h) — check the species tables for the indication
- **Routes:** PO
- **Last reviewed:** 1 October 2026

## Indications

- Canine pituitary-dependent hyperadrenocorticism
- Canine adrenal-dependent hyperadrenocorticism
- Feline hyperadrenocorticism (off-label)
- Alopecia X (some cases)

## Trilostane dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Dogs

*Trilostane doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Hyperadrenocorticism (starting dose) | 1–3 mg/kg | PO | start ~2 mg/kg q24h with food; many dogs do better split q12h | — |
| Alopecia X | 3–12 mg/kg | PO | q12–24h (daily total) | — |

- Hyperadrenocorticism (starting dose): Papich 5e: label 2.2–6.7 mg/kg once daily PO, but many dogs are controlled starting at 0.5–1 mg/kg q12h (or 2–3 mg/kg once daily), increased to 1.5–3.8 mg/kg q12h by testing; large dogs may need less per kg. Plumb’s p.1146: label 2.2–6.7 mg/kg PO once daily with food; to switch to twice daily increase the total daily dose by ⅓–½ and divide; 1 mg/kg once daily start (Feldman 2007). ACTH stimulation 4–6 h post-dose at 10–14 days, 30 and 90 days, then every 3–6 months; stop for 48–72 h and restart lower if post-ACTH cortisol is too low. Monitor electrolytes.
- Alopecia X: Papich 5e: 9–12 mg/kg/day PO. Plumb’s p.1146: Alaskan Malamutes 3–3.6 mg/kg PO twice daily for 4–6 months (Leone 2005); Miniature Poodles and Pomeranians average 10.85 mg/kg/day once daily or divided (Cerundolo 2004). Monitor as for Cushing’s.

### Cats

*Trilostane doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Hyperadrenocorticism (off-label) | 1–5 mg/kg | PO | q12–24h; titrate to ACTH stim | — |

- Hyperadrenocorticism (off-label): Papich 5e: start 1–2 mg/kg/day PO, increasing as needed to 3–6 mg/kg q24h (most cats 10–30 mg per cat daily); or 3 mg/kg q12h increasing to 5 mg/kg q12h. Plumb’s p.1146: 7 mg/kg/day divided twice daily (Greco 2007); 15 mg once daily to 60 mg q12h per cat (Scott-Moncrieff 2010). Titrate with ACTH stimulation tests; cats usually remain diabetic.

### Horses

*Trilostane doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Pituitary pars intermedia dysfunction (Cushing’s) | 0.4–1 mg/kg | PO | q24h (in feed) | — |

- Pituitary pars intermedia dysfunction (Cushing’s): Papich 5e and Plumb’s p.1146 (McGowan & Neiger 2003): 0.4–1 mg/kg (120–240 mg total) PO once daily, added to feed.

## Contraindications

Primary hepatic or renal disease. Pregnancy (do not handle if pregnant — affects steroidogenesis). Concurrent potassium-sparing drugs / ACE inhibitors increase hyperkalaemia risk. Do not use with mitotane simultaneously.

## Adverse effects

- Lethargy, inappetence, vomiting, diarrhoea
- Hypocortisolaemia / iatrogenic hypoadrenocorticism — collapse, hyperkalaemia
- Rare adrenal necrosis causing permanent Addison’s

## Drug interactions

- ACE inhibitors / potassium-sparing diuretics (e.g. spironolactone): additive hyperkalaemia risk
- Mitotane: do not use concurrently — additive, unpredictable adrenal suppression
- Ketoconazole: additional inhibition of steroidogenesis (additive cortisol lowering)

## Pregnancy and lactation

Contraindicated in pregnancy; pregnant staff should not handle opened capsules.

## Monitoring

- ACTH-stimulation test 4–6 h post-dose at 10–14 days, 4 weeks, 12 weeks, then 3-monthly
- Electrolytes (watch for hyperkalaemia / hyponatraemia = adrenal insufficiency)
- Clinical signs — appetite, water intake, demeanour

## Toxicity and overdose

Excessive cortisol suppression causes iatrogenic hypoadrenocorticism — lethargy, vomiting, diarrhoea, collapse, hyponatraemia and hyperkalaemia; rarely irreversible adrenal necrosis producing permanent Addison’s disease.

Management: Stop trilostane. For a hypoadrenocortical crisis: IV 0.9 % saline, dexamethasone (or hydrocortisone), treat hyperkalaemia (calcium gluconate, dextrose ± insulin), and re-test ACTH stimulation before resuming at a lower dose. The short half-life means the effect reverses as the drug clears.

## Clinical pearls

- Any lethargy, vomiting or anorexia in a trilostane patient is a possible hypoadrenocortical crisis — stop the drug, check electrolytes and an ACTH stim before resuming
- Give with food and recheck ACTH stimulation 4–6 hours after dosing to time it correctly
- Splitting the daily dose twice-daily often gives smoother cortisol control than a single dose

## Mechanism of action

Reversibly and competitively inhibits 3-β-hydroxysteroid dehydrogenase in the adrenal cortex, blocking conversion of pregnenolone to progesterone and thereby the synthesis of cortisol (and, to a lesser extent, aldosterone and adrenal sex steroids). The block is dose-dependent and reversible, allowing titratable control of hypercortisolaemia.

## Formulations and products

- Vetoryl 5 mg capsule
- Vetoryl 10 mg capsule
- Vetoryl 30 mg capsule
- Vetoryl 60 mg / 120 mg capsule
- Vetoryl (Dechra) — 5 / 10 / 30 / 60 / 120 mg, Capsule

## Storage

Store capsules at 15–25 °C, dry. Do not open or crush; pregnant staff must not handle the contents.

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

## Other hormones, emergency drugs, supplements and other drugs

- [Thiamine (Vitamin B1)](https://vetmasterji.com/drugs/thiamine)
- [Toceranib](https://vetmasterji.com/drugs/toceranib)
- [Toldimfos sodium (Organic Phosphorus)](https://vetmasterji.com/drugs/toldimfos)
- [Tranexamic Acid](https://vetmasterji.com/drugs/tranexamic-acid)
- [Vinblastine](https://vetmasterji.com/drugs/vinblastine)
- [Vincristine](https://vetmasterji.com/drugs/vincristine)
- [Vitamin AD3E Injection](https://vetmasterji.com/drugs/vitamin-ad3e-injection)
- [Vitamin E / Selenium](https://vetmasterji.com/drugs/vitamin-e-selenium)

## Frequently asked questions

### What is the dose of Trilostane for dogs?

Reference doses for Trilostane in dogs: 1–3 mg/kg PO start ~2 mg/kg q24h with food; many dogs do better split q12h (Hyperadrenocorticism (starting dose)); 3–12 mg/kg PO q12–24h (daily total) (Alopecia X). Confirm against the label and the patient before use.

### What is the dose of Trilostane for cats?

Reference doses for Trilostane in cats: 1–5 mg/kg PO q12–24h; titrate to ACTH stim (Hyperadrenocorticism (off-label)). Confirm against the label and the patient before use.

### What is the dose of Trilostane for horses?

Reference doses for Trilostane in horses: 0.4–1 mg/kg PO q24h (in feed) (Pituitary pars intermedia dysfunction (Cushing’s)). Confirm against the label and the patient before use.

### When should Trilostane not be used?

Primary hepatic or renal disease. Pregnancy (do not handle if pregnant — affects steroidogenesis). Concurrent potassium-sparing drugs / ACE inhibitors increase hyperkalaemia risk. Do not use with mitotane simultaneously.

### What are the side effects of Trilostane in animals?

Lethargy, inappetence, vomiting, diarrhoea; Hypocortisolaemia / iatrogenic hypoadrenocorticism — collapse, hyperkalaemia; Rare adrenal necrosis causing permanent Addison’s.

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

---

VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.