Trilostane
Trilostane controls hypercortisolism by reversibly reducing adrenal steroid synthesis. It does not remove an adrenal tumour.
Group
Adrenal steroid synthesis inhibitor
Mechanism of Action
Competitively inhibits 3-beta-hydroxysteroid dehydrogenase and reduces cortisol and, variably, aldosterone/progesterone synthesis.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Hyperadrenocorticism — Initial | 0.5–1 mg/kg | PO | Every 12 h | Lower-dose twice-daily starting alternative; titrate by clinical response and cortisol/electrolyte monitoring. |
| Hyperadrenocorticism — Initial | 2–3 mg/kg | PO | Every 24 h | Separate once-daily starting alternative; do not add to the twice-daily regimen. |
| Hyperadrenocorticism — Maintenance | 1.5–3.8 mg/kg | PO | Every 12 h | Titrated range described in the source, not an automatic target. Stop and reassess for adverse signs. |
| Hyperadrenocorticism – capsule label alternative — Initial | 2.2–6.7 mg/kg | PO | Every 24 h | Higher capsule-label starting range in the supplied references; distinct from the lower-dose starting approaches. Give with food and monitor closely. |
| Hyperadrenocorticism – low once-daily alternative — Initial | 1 mg/kg | PO | Every 24 h | Source describes recheck after approximately one week, with clinical assessment and cortisol testing. |
| Alopecia X – Alaskan Malamute | 3–3.6 mg/kg | PO | Every 12 h | Small study used 4-6 months of treatment; monitor adrenal function. |
| Alopecia X – historical daily regimen | 9–12 mg/kg | PO | Every 24 h | Historical adjunct; source also reports a mean 10.85 mg/kg/day given once or divided twice daily for 4-8 weeks. Evidence and benefit require individual assessment. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Hyperadrenocorticism — Initial | 1–2 mg/kg | PO | Every 24 h | Titrate with ACTH/cortisol and clinical response; diabetes may persist. |
| Hyperadrenocorticism — Maintenance | 3–6 mg/kg | PO | Every 24 h | Separate source titrated range; most cats in that source receive about 10-30 mg per cat daily, not an additional dose. |
| Hyperadrenocorticism – twice-daily alternative — Initial | 3 mg/kg | PO | Every 12 h | Reassess before titrating up to 5 mg/kg every 12 hours. |
| Hyperadrenocorticism – twice-daily alternative — Maintenance | 5 mg/kg | PO | Every 12 h | |
| Hyperadrenocorticism – historical divided regimen | 3.5 mg/kg | PO | Every 12 h | Converted from 7 mg/kg/day divided twice daily; source mentions total daily amounts up to 60 mg in a small series. |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Historical hypercortisolism adjunct | 0.4–1 mg/kg | PO | Every 24 h | Historical regimen; not established as preferred treatment for equine PPID. |
Indications
- Canine hyperadrenocorticism
- Selected feline hyperadrenocorticism
- Historical equine or alopecia adjuncts
Contraindications
- Do not use in pregnancy.
- Avoid use in primary hepatic disease or renal insufficiency where excluded by the selected product; assess electrolytes and hydration before treatment.
Interactions
- ACE inhibitors, potassium-sparing diuretics or potassium supplements increase hyperkalaemia risk.
- Mitotane, ketoconazole and other adrenal inhibitors can intensify adrenal suppression.
Adverse effects
- Vomiting, diarrhoea, anorexia and lethargy.
- Hypoadrenocorticism, hyperkalaemia/hyponatraemia and, rarely, persistent adrenal injury or death.
Toxicity
Withhold treatment if anorexia, vomiting, collapse or marked lethargy develops. Assess cortisol/electrolytes and provide fluid and corticosteroid support when adrenal insufficiency is suspected.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Vetoryl 10 mg hard capsule Administer whole with food; do not open or split capsule contents. | Capsule | 10 mg / capsule | PO |
| Vetoryl 30 mg hard capsule Administer whole with food; do not open or split capsule contents. | Capsule | 30 mg / capsule | PO |
| Vetoryl 60 mg hard capsule Administer whole with food; do not open or split capsule contents. | Capsule | 60 mg / capsule | PO |
| Vetoryl 120 mg hard capsule Administer whole with food; do not open or split capsule contents. | Capsule | 120 mg / capsule | PO |
Monitoring and Administration
Give with food. Recheck about 10-14 days after starting or changing dose and thereafter at approximately 30 days, 90 days and three-month intervals according to stability.
Interpret clinical signs together with timed cortisol/ACTH testing, electrolytes and renal/hepatic function. The sources use different testing targets and timing; use one internally consistent monitoring protocol rather than combining cutoffs.
Do not open or divide capsules; pregnant people should not handle them. Large dogs may need a lower mg/kg dose than small dogs.
Treat hypokalaemia or hyperkalaemia only from measured results; trilostane-associated aldosterone suppression usually raises concern for hyperkalaemia, not an automatic need for potassium supplements.