Home/Medicines/Trilostane

Trilostane

Prescription

Adrenal steroidogenesis inhibitor (3-beta-hydroxysteroid dehydrogenase inhibitor)

Last reviewed 19 Apr 2026 · PetCare.AI Editorial Team

Species

Dog, Cat

Brands

2 available

Interactions

5 documented

Formulations

Mechanism of action

Competitively inhibits 3-beta-hydroxysteroid dehydrogenase in the adrenal cortex, blocking conversion of pregnenolone to progesterone and reducing cortisol synthesis

At a glance

Class

Adrenal steroidogenesis inhibitor (3-beta-hydroxysteroid dehydrogenase inhibitor)

Schedule

Prescription

Storage

Store below 25°C; do not open capsules (human absorption risk — wear gloves if handling powder)

Dosing

🐕

Dog

Pituitary-dependent hyperadrenocorticism (Cushing's disease)

Dose

1–3 mg/kg

Route

Frequency

SID (may increase to BID)

Max dose

120 mg/dose; 240 mg/day

Duration: Life-long; give with food; ACTH stim test at 10 days, 4 weeks, 12 weeks

🐈

Cat

Hyperadrenocorticism (rare in cats)

Dose

1–3 mg/kg

Route

Frequency

SID

Max dose

30 mg

Duration: Long-term; limited data in cats

Educational reference only

This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →

Formulations

💊

Capsule — 4

Strength

10mg

Strength

30mg

Strength

60mg

Strength

120mg

Storage

Store below 25°C; do not open capsules (human absorption risk — wear gloves if handling powder)

Safety

Absolute contraindications — do not use

Primary hepatic disease
May confound monitoring
Renal insufficiency
Risk of Addisonian crisis

Use with caution

Concurrent potassium-sparing drugs
Risk of hyperkalemia from adrenal suppression

Adverse effects

Common

Anorexia

Lethargy

Vomiting

Diarrhoea

Serious

Addisonian crisis (adrenal necrosis)

Hypoadrenocorticism

Electrolyte imbalances

Sudden death (rare)

Monitoring parameters

ACTH stimulation test (post-cortisol target 1.5–5.5 mcg/dL)Electrolytes (Na, K)Renal valuesClinical signs (PU/PD, appetite, coat)

Educational reference only

Interactions

Major — 2

Ketoconazole

major

Both inhibit adrenal steroidogenesis; combined use risks severe hypoadrenocorticism (Addisonian crisis)

Management: Do not use concurrently. Allow adequate washout between drugs.

Spironolactone

major

Trilostane reduces cortisol; spironolactone is an aldosterone antagonist. Combined adrenal suppression risks Addisonian crisis.

Management: Avoid concurrent use unless under specialist supervision with frequent ACTH stimulation testing.

Moderate — 3

Ketoconazole (Systemic)

moderate

Both ketoconazole and trilostane inhibit adrenal steroidogenesis. Combined use may cause profound hypocortisolism.

Management: Avoid concurrent use. If transitioning between agents, monitor ACTH stimulation test closely.

Benazepril

moderate

Trilostane reduces aldosterone + ACE inhibitor reduces aldosterone: combined potassium-retaining effect.

Management: Monitor serum potassium. Clinically used combination in Cushing's dogs with concurrent heart disease — requires monitoring.

Prednisolone

moderate

Trilostane inhibits adrenal cortisol synthesis. Exogenous prednisolone supplementation may be needed during Addisonian crisis but interferes with ACTH stimulation test interpretation.

Management: Keep prednisolone available for emergency (Addisonian crisis). When performing ACTH stim test for trilostane monitoring, withhold prednisolone for 24h before test.

Educational reference only

Brands

International

Vetoryl

Dechra

Modrenal

Bioenvision

FAQs

Frequently asked questions

›What is Trilostane?

Trilostane is a adrenal steroidogenesis inhibitor (3-beta-hydroxysteroid dehydrogenase inhibitor) used in pets. Competitively inhibits 3-beta-hydroxysteroid dehydrogenase in the adrenal cortex, blocking conversion of pregnenolone to progesterone and reducing cortisol synthesis

›What is Trilostane used for in pets?

Trilostane is used in veterinary medicine for: Pituitary-dependent hyperadrenocorticism (Cushing's disease); Hyperadrenocorticism (rare in cats).

›What is the Trilostane dose for dogs?

For dogs, Trilostane is typically dosed as follows — Pituitary-dependent hyperadrenocorticism (Cushing's disease): 1–3 mg/kg PO SID (may increase to BID). Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.

›What is the Trilostane dose for cats?

For cats, Trilostane is typically dosed as follows — Hyperadrenocorticism (rare in cats): 1–3 mg/kg PO SID. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.

›What are the side effects of Trilostane?

Common: Anorexia, Lethargy, Vomiting, Diarrhoea. Serious (call your vet immediately): Addisonian crisis (adrenal necrosis), Hypoadrenocorticism, Electrolyte imbalances, Sudden death (rare).

›Does Trilostane need a prescription?

Yes. Trilostane is a prescription medication and should only be administered under veterinary supervision.

›When should Trilostane not be used?

Do not use Trilostane if: Primary hepatic disease; Renal insufficiency.

Educational reference only

References

The PetCare.AI drug reference is built from 13 authoritative sources cited across 580 drug monographs.

Textbooks & handbooks — 5

Plumb's Veterinary Drug Handbook
Withrow & MacEwen's Small Animal Clinical Oncology
Merck Veterinary Manual
NRC Nutrient Requirements of Dogs and Cats
Veterinary Pharmacology and Therapeutics (Riviere & Papich)

Clinical guidelines & consensus — 4

ASPCA Animal Poison Control Center Guidelines
AAHA Diabetes Management Guidelines
ASPCA Poison Control Guidelines
RECOVER CPR Guidelines

Journals & peer-reviewed studies — 2

EPIC Study (J Vet Intern Med 2016)
JVIM FAT CAT Study

Regulatory & approvals — 1

CDSCO Veterinary Drug Approval Registry (1969–2026)

Databases — 1

Washington State University VCPL MDR1 Database

Related medicines

Other medicines in the same class (Adrenal steroidogenesis inhibitor).

Metyrapone

Inhibits 11-beta-hydroxylase, the enzyme catalyzing the final step of cortisol synthesis (11-deoxycortisol → cortisol). Used diagnostically to test pituitary ACTH reserve and therapeutically to reduce cortisol in Cushing's syndrome.

dogcat