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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
4

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
PO
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
PO
Frequency
SID
Max dose
30 mg
Duration: Long-term; limited data in cats

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)

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.

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.

References

References

Textbooks & handbooks

  • Plumb, D.C. Plumb's Veterinary Drug Handbook. 10th ed., Wiley-Blackwell, 2023.
  • Vail, D.M., Thamm, D.H., & Liptak, J.M. (eds.). Withrow & MacEwen's Small Animal Clinical Oncology. 6th ed., Saunders/Elsevier, 2020.
  • Riviere, J.E., & Papich, M.G. (eds.). Veterinary Pharmacology and Therapeutics. 10th ed., Wiley-Blackwell, 2018.
  • National Research Council. Nutrient Requirements of Dogs and Cats. National Academies Press, Washington DC, 2006.
  • The Merck Veterinary Manual. Merck & Co., Online edition. https://www.merckvetmanual.com/

Clinical guidelines & consensus

  • Fletcher, D.J., Boller, M., Brainard, B.M., et al. "RECOVER Evidence and Knowledge Gap Analysis on Veterinary CPR." Journal of Veterinary Emergency and Critical Care, 2012;22(S1):S102–S131.
  • American Animal Hospital Association. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. AAHA Press.

Journals & peer-reviewed studies

  • Hogan, D.F., Fox, P.R., Jacob, K., et al. "Secondary prevention of cardiogenic arterial thromboembolism in the cat: The FAT CAT study." Journal of Veterinary Cardiology, 2015;17(Suppl 1):S306–S317.
  • Boswood, A., Häggström, J., Gordon, S.G., et al. "Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study — A Randomized Clinical Trial." Journal of Veterinary Internal Medicine, 2016;30(6):1765–1779.
  • ASPCA Animal Poison Control Center. Toxicology and Poison Management Guidelines. American Society for the Prevention of Cruelty to Animals. https://www.aspca.org/pet-care/animal-poison-control

Regulatory & approvals

  • Central Drugs Standard Control Organisation (CDSCO), Government of India. Veterinary Drug Approval Registry, 1969–2026. Directorate General of Health Services. https://cdsco.gov.in/

Databases

  • Washington State University, College of Veterinary Medicine. Veterinary Clinical Pharmacology Laboratory (VCPL) — MDR1 Multidrug Sensitivity Database. https://vcpl.vetmed.wsu.edu/
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 →

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