Canine Cushing’s Disease: Trilostane Dosing & Monitoring Guide

You manage canine Cushing’s disease with regular ACTH stimulation tests every 3–6 months, aiming for post-ACTH cortisol levels between 1.0 and 5.5 µg/dL. Trilostane, given at 1–3 mg/kg orally once or twice daily, blocks cortisol production by inhibiting 3-beta-hydroxysteroid dehydrogenase. Watch for vomiting, lethargy, or appetite loss, which may signal adrenal insufficiency. Monitor electrolytes due to potential aldosterone disruption. Keep water intake under 100 mL/kg/day. There’s more to optimizing long-term outcomes.

Notable Insights

• Diagnose Cushing’s disease using ACTH stimulation or low-dose dexamethasone tests after screening with urine cortisol-to-creatinine ratios.
• Trilostane controls cortisol production by inhibiting steroid synthesis and is used for both pituitary- and adrenal-dependent forms.
• Administer trilostane orally at 1–3 mg/kg once or twice daily, adjusting dose based on ACTH stimulation test results.
• Monitor for side effects like lethargy, vomiting, and appetite loss, and check electrolytes due to potential aldosterone impact.
• Recheck ACTH stimulation tests every 3–6 months and track water intake and urine specific gravity for treatment adjustments.

What Is Cushing’s Disease in Dogs?

Cushing’s disease, also known as hyperadrenocorticism, is a hormonal disorder that affects your dog’s adrenal glands. It results in excessive cortisol production, disrupting normal metabolism and immune function. Most cases stem from a pituitary adenoma-a benign tumor in the pituitary gland-accounting for 80% to 85% of instances. This tumor secretes adrenocorticotropic hormone (ACTH), overstimulating the adrenal glands. Less commonly, an adrenal tumor directly produces excess cortisol, usually unilateral and palpable via imaging. Adrenal-dependent cases make up 15% to 20%. These tumors may be malignant or benign, detectable through abdominal ultrasound. The condition progresses slowly, primarily affecting middle-aged to older dogs. Diagnosis requires hormonal testing, such as the low-dose dexamethasone suppression test or ACTH stimulation test. Understanding the origin-pituitary versus adrenal-is critical for treatment planning and prognosis. Early differentiation guides therapeutic decisions, including medication or surgery.

What Symptoms Does Cushing’s Cause in Dogs?

You’ll notice gradual changes in your dog’s behavior and body as excess cortisol disrupts normal physiological processes. Increased thirst is one of the most consistent signs, with dogs often consuming 2–3 times the normal volume of water daily. This leads to frequent urination and potential indoor accidents. Hair loss occurs symmetrically, especially along the trunk, tail, and rear limbs, due to cortisol-induced inhibition of hair follicle cycles. The skin thins, feels fragile, and may develop dark pigmentation. Your dog might develop a pot-bellied appearance from fat redistribution and weakened abdominal muscles. Muscle atrophy contributes to lethargy and reduced exercise tolerance. Panting becomes persistent, even at rest, due to altered respiratory mechanics and metabolic demand. Appetite increases in about 80% of affected dogs. These symptoms progress slowly over months, mimicking aging. Early recognition improves long-term management outcomes markedly.

How Do Vets Diagnose Cushing’s Disease?

How do veterinarians confirm a condition that mimics so many other ailments? Your vet starts with bloodwork and urinalysis to rule out common diseases with similar signs. Elevated liver enzymes and dilute urine often prompt suspicion of Cushing’s. The urine cortisol-to-creatinine ratio is a sensitive screening tool-dogs with Cushing’s typically show elevated urine cortisol levels, though stress can cause false positives. For confirmation, the ACTH stimulation test is the gold standard. Your dog receives an injection of synthetic ACTH, and blood cortisol is measured before and one hour after. A post-ACTH cortisol level above 20 µg/dL confirms hyperadrenocorticism. This test is reliable and widely available. While it can’t differentiate between pituitary and adrenal forms, it confirms adrenal overactivity.

How Does Trilostane Treat Cushing’s in Dogs?

Trilostane works by blocking a key enzyme in the adrenal glands called 3-beta-hydroxysteroid dehydrogenase, which is essential for cortisol production. This inhibition is the core of the trilostane mechanism, directly interfering with the synthesis of cortisol from its precursors. By suppressing overactive adrenal pathways, trilostane achieves effective cortisol suppression in dogs with Cushing’s disease. The drug targets both adrenal and pituitary-dependent forms, reducing symptoms like excessive thirst, urination, and panting. Trilostane is administered orally once or twice daily, with dosing typically starting at 1–3 mg/kg. Peak plasma concentrations occur within 2–4 hours post-administration. It’s rapidly metabolized, with a half-life of about 1.5 hours, but its enzyme-inhibiting effects last longer. Consistent dosing maintains steady cortisol control. This targeted approach allows medical management without destroying adrenal tissue.

What Side Effects Should You Watch for on Trilostane?

Most dogs tolerate trilostane well, but side effects can occur and require close monitoring. Adrenal suppression is a primary concern, happening when trilostane over-inhibits cortisol production. This can lead to lethargy, vomiting, or collapse. You’ll need to watch for weakness or sudden appetite loss-these are red flags. Trilostane affects steroid synthesis, so adrenal function must stay balanced. Electrolyte imbalance may develop due to altered aldosterone levels, influencing sodium and potassium. Look for increased thirst, frequent urination, or dehydration. In severe cases, hyponatremia or hyperkalemia can compromise heart and muscle function. These shifts are measurable via blood tests, especially ACTH stimulation tests and electrolyte panels. Never adjust the dose without veterinary guidance. If side effects appear, discontinue trilostane immediately and contact your vet. Early detection prevents emergencies.

How to Manage Cushing’s Long-Term With Vet Care and Testing

While Cushing’s disease can’t be cured, consistent veterinary oversight makes long-term management achievable. You’ll need regular ACTH stimulation tests every 3–6 months to assess cortisol levels and adjust trilostane dosage accurately. Ideal control targets post-ACTH serum cortisol between 1.0–5.5 µg/dL. Diet management plays a critical role-feed a low-fat, high-fiber, high-quality protein diet to counteract muscle wasting and reduce metabolic strain. Therapeutic veterinary diets like Hill’s l/d or Royal Canin Veterinary Diet Early Renal Support are formulated for these metabolic demands. Exercise routines should be moderate and consistent, supporting weight control and insulin sensitivity without inducing stress. Avoid overexertion, which can elevate cortisol. Monitor water intake (normal is <100 mL/kg/day) and urine specific gravity to detect changes early. Radiographs or ultrasounds may be needed if abdominal enlargement progresses.

On a final note

You control Cushing’s disease with consistent trilostane therapy and monitoring. Trilostane inhibits 3β-hydroxysteroid dehydrogenase, reducing cortisol synthesis. Administer once or twice daily, typically at 2.2–6.7 mg/kg orally. Monitor ACTH stimulation tests every 10–14 days initially, then every 3–6 months. Watch for lethargy, vomiting, or diarrhea-signs of hypocortisolism. Adjust dosage based on post-pill cortisol levels. Regular bloodwork and clinical observation guarantee proper management and prevent complications.