Trilostane for Cushing's in Dogs: Complete Treatment & Dosing Guide

What Is Cushing's Disease and How Does Trilostane Help?

Hyperadrenocorticism — commonly called Cushing's disease — occurs when a dog's body produces excessive cortisol over a prolonged period. In roughly 80–85% of cases, the cause is a benign pituitary tumor (pituitary-dependent hyperadrenocorticism, or PDH) that overstimulates the adrenal glands. The remaining 15–20% stem from adrenal tumors (adrenal-dependent hyperadrenocorticism, or ADH) that independently overproduce cortisol. Cushing's is one of the most common endocrine disorders in middle-aged to older dogs, with an estimated prevalence of 1 to 2 cases per 1,000 dogs annually, according to the Merck Veterinary Manual.

Trilostane (brand name Vetoryl) is the only FDA-approved medication for treating both pituitary-dependent and adrenal-dependent Cushing's disease in dogs. It works by inhibiting the enzyme 3β-hydroxysteroid dehydrogenase, which blocks a critical step in cortisol synthesis within the adrenal glands. Unlike older options like mitotane (Lysodren), which permanently destroys adrenal tissue, trilostane reversibly suppresses cortisol production — making it a more controllable, adjustable therapy. Since its FDA approval in 2008, trilostane has become the first-line medical treatment for canine Cushing's disease worldwide.

Disclaimer: This guide is for educational purposes. Always consult your veterinarian before starting, adjusting, or stopping any medication for your dog. Only a licensed veterinarian can diagnose Cushing's disease and prescribe trilostane.

Recognizing Cushing's Disease: Symptom Checklist by Severity

Cushing's disease develops gradually, and early signs are easy to dismiss as normal aging. Recognizing the progression pattern helps you catch it sooner. The following checklist organizes clinical signs from early warning indicators to advanced-stage symptoms that signal urgent veterinary attention.

Which Dogs Are Most at Risk for Cushing's Disease?

How Veterinarians Diagnose Cushing's Disease

Diagnosing Cushing's disease is a multi-step process. No single test provides a definitive answer in every case, and false positives can occur in dogs with other illnesses (a phenomenon called "stress hypercortisolism"). Your veterinarian will typically follow a structured diagnostic pathway:

1. Initial Screening — Bloodwork and Urinalysis ($150–$300): A complete blood count (CBC), chemistry panel, and urinalysis may reveal elevated liver enzymes (especially ALP), high cholesterol, dilute urine, and sometimes elevated blood sugar. These findings raise suspicion but are not diagnostic on their own.
2. Low-Dose Dexamethasone Suppression Test (LDDST) ($100–$250): Considered the gold-standard screening test. Your dog receives a small injection of dexamethasone, and blood cortisol levels are measured at 0, 4, and 8 hours. In a healthy dog, dexamethasone suppresses cortisol production. In a Cushing's dog, cortisol remains elevated. This test requires an 8-hour clinic stay.
3. ACTH Stimulation Test ($80–$200): Measures the adrenal glands' response to synthetic ACTH. Less sensitive than the LDDST for PDH (misses roughly 20–30% of cases) but highly specific — a positive result strongly confirms Cushing's. Also used to monitor trilostane treatment response. This test takes 1–2 hours.
4. Urine Cortisol:Creatinine Ratio ($50–$100): A non-invasive screening test done on a morning urine sample collected at home. A normal result effectively rules out Cushing's, but an elevated result requires follow-up testing since stress and other diseases can also elevate this ratio.
5. High-Dose Dexamethasone Suppression Test (HDDST) ($100–$200): Helps differentiate PDH from ADH after Cushing's is confirmed. In PDH, high-dose dexamethasone partially suppresses cortisol; in ADH, it typically does not.
6. Abdominal Ultrasound ($300–$600): Visualizes the adrenal glands. Bilaterally enlarged adrenals suggest PDH; one enlarged and one atrophied gland suggests an adrenal tumor. Also screens for other abdominal abnormalities. Performed by your vet or a veterinary specialist.
7. Endogenous ACTH Level ($60–$120): A blood test that helps differentiate PDH (high ACTH) from ADH (low ACTH). Sample handling is critical — the blood must be processed and frozen quickly.

Trilostane Treatment: Dosing, Monitoring, and What to Expect

How Trilostane Works

Trilostane (Vetoryl) is a competitive inhibitor of the enzyme 3β-hydroxysteroid dehydrogenase. This enzyme is essential for converting pregnenolone to progesterone — a key step in the cortisol synthesis pathway. By blocking this conversion, trilostane reduces the amount of cortisol the adrenal glands can produce. The effect is reversible: if the medication is stopped, cortisol production resumes. This reversibility is one reason trilostane is preferred over mitotane, which causes permanent adrenal cell destruction.

Dosing Guidelines

Trilostane is administered orally, once or twice daily, and must be given with food to maximize absorption. The starting dose has shifted lower over the years as veterinary endocrinologists have found that conservative dosing achieves good control with fewer side effects.

These are general starting ranges. Your veterinarian will determine the exact dose based on your dog's baseline cortisol levels, body condition, and clinical signs. Many veterinarians now start at the lower end and titrate upward based on ACTH stimulation test results, rather than starting at a higher weight-based dose. The manufacturer's labeled starting dose is 1–3 mg/kg once daily, but many clinicians use 0.5–1 mg/kg twice daily for more stable cortisol control throughout the day.

The Monitoring Schedule — What Your First Year Looks Like

Monitoring is non-negotiable with trilostane. Too little medication leaves Cushing's uncontrolled; too much can cause an Addisonian crisis (acute cortisol deficiency), which is life-threatening. Here is a typical monitoring timeline:

• 10–14 days after starting: First ACTH stimulation test and clinical recheck. Your vet will assess cortisol levels and adjust the dose if needed.
• 30 days: Second ACTH stim test and recheck. Most dogs reach a stable dose by this point.
• 60 days: Third ACTH stim test. If cortisol is well-controlled, monitoring intervals lengthen.
• 90 days: Recheck with ACTH stim and chemistry panel.
• Every 3–6 months thereafter: Ongoing monitoring for the rest of your dog's life. Some dogs need dose adjustments over time as their disease progresses or their metabolism changes.

Each ACTH stimulation test and recheck visit typically costs $150–$350, depending on your area and whether additional bloodwork is included. Budget approximately $800–$1,500 in monitoring costs during the first year, then $400–$800 per year for ongoing checks.

Signs the Dose Is Working

You should notice improvements in this general order:

1. Within 1–2 weeks: Drinking and urination begin to decrease — often the first and most noticeable improvement
2. Within 2–4 weeks: Appetite normalizes; panting may decrease
3. Within 1–3 months: Activity level improves; pot-bellied appearance starts to reduce as abdominal muscle tone returns
4. Within 3–6 months: Coat regrowth begins (often the slowest change); skin thickens and infections clear

Treatment Comparison: Trilostane vs. Other Options

Side Effects, Risks, and When to Call the Vet

Most dogs tolerate trilostane well, but side effects can occur — especially during dose adjustment periods. Understanding the difference between mild side effects and emergency symptoms is critical.

Prognosis and Life Expectancy with Trilostane Treatment

Most dog owners' first question after a Cushing's diagnosis is: "How long will my dog live?" The answer depends on the type of Cushing's, how early it was caught, and how well the disease responds to treatment.

According to the American Kennel Club, many dogs with well-managed pituitary-dependent Cushing's disease go on to live full, comfortable lives for years after diagnosis. The key variables are consistent medication administration, strict adherence to the monitoring schedule, and early intervention when side effects appear.

Managing Cushing's at Home: Daily Care and Lifestyle Adjustments

Living with a Cushing's dog on trilostane involves more than just giving a pill each morning. Here are the daily and long-term management strategies that make the biggest difference:

Medication Administration Best Practices

• Always give trilostane with food. Absorption is significantly improved when the capsule is given with a meal. Some veterinarians recommend splitting the dose into twice-daily administration (morning and evening) for more stable cortisol levels.
• Give at the same time every day. Consistency matters for both cortisol control and accurate ACTH stimulation testing.
• Never adjust the dose on your own. Even small dose changes can tip the balance toward an Addisonian crisis or leave Cushing's uncontrolled.
• Keep a medication log. Note the time given, whether your dog ate it fully, and any observations about behavior, thirst, or appetite. This log is invaluable during recheck visits.

Monitoring Water Intake and Urination

Track your dog's daily water consumption. A useful benchmark: normal water intake is approximately 50–60 mL per kg of body weight per day (roughly 1 ounce per pound). A 30-lb (13.6 kg) dog should drink about 680–820 mL (roughly 3–3.5 cups) daily. Cushing's dogs often drink 2–5 times this amount before treatment. As trilostane takes effect, you should see intake trending downward. If drinking suddenly increases again, it may signal that the dose needs adjustment.

Diet and Exercise Considerations

• Diet: Feed a balanced, moderate-protein, moderate-fat diet. Cushing's dogs are prone to pancreatitis and elevated liver enzymes, so avoid high-fat table scraps and rich treats. A veterinary-formulated diet for metabolic or hepatic support may be recommended by your vet.
• Exercise: Maintain regular, moderate exercise as your dog's energy allows. Muscle wasting improves with treatment, and gentle activity helps rebuild strength. Avoid intense exercise until your dog has been stable on trilostane for at least 2–3 months.
• Weight management: Monitor body condition score (BCS). The pot-bellied appearance should gradually improve, but some dogs gain weight once cortisol normalizes. Adjust food portions as needed with your vet's guidance.

Skin and Coat Care

Coat regrowth is often the slowest improvement — it can take 3–6 months or longer. In the meantime, keep the skin clean and monitor for secondary bacterial or yeast infections (red, itchy, or smelly patches). Medicated shampoos containing chlorhexidine or ketoconazole may be recommended by your veterinarian for recurring skin infections. Never shave a Cushing's dog's coat unless medically necessary, as the hair may not regrow properly.

The True Cost of Trilostane Treatment: Budgeting for Your Dog's Care

Cushing's disease is a chronic condition requiring lifelong management. Here is a realistic cost breakdown so you can plan accordingly:

Costs vary significantly by region, clinic type (general practice vs. specialty), and your dog's dose requirements. Larger dogs cost more to treat because they need higher doses and larger capsule sizes. Pet insurance can offset some of these costs if Cushing's was not a pre-existing condition when the policy was purchased — check your policy's endocrine disorder coverage limits.

Frequently Asked Questions About Trilostane for Cushing's in Dogs

Can Cushing's disease in dogs be cured?

In most cases (pituitary-dependent Cushing's), the disease is managed rather than cured. Trilostane controls cortisol levels but does not eliminate the underlying pituitary tumor. Dogs require lifelong medication and monitoring. Adrenal-dependent Cushing's caused by a benign adrenal tumor can sometimes be cured through surgical removal of the affected gland, though this is a complex procedure with inherent risks.

How long does it take for trilostane to work?

Most owners notice reduced drinking and urination within 1–2 weeks of starting trilostane. Full clinical improvement — including coat regrowth and muscle recovery — typically takes 2–6 months. The first ACTH stimulation test is usually performed 10–14 days after starting treatment to verify that cortisol levels are responding appropriately.

Can I stop trilostane once my dog seems better?

No. Trilostane controls Cushing's symptoms by suppressing cortisol production — it does not cure the disease. Stopping the medication will cause cortisol levels to rise again, and symptoms will return within days to weeks. Never discontinue trilostane without your veterinarian's explicit guidance.

What happens if I miss a dose of trilostane?

Missing a single dose is generally not dangerous. Give the next dose at the regularly scheduled time — do not double up. If you miss multiple consecutive doses, contact your veterinarian, as cortisol levels may have risen enough to warrant re-evaluation before resuming at the previous dose.

Are there any drug interactions with trilostane?

Yes. Trilostane can interact with several medications. ACE inhibitors (like enalapril or benazepril), potassium-sparing diuretics (like spironolactone), and potassium supplements can increase the risk of hyperkalemia (dangerously high potassium levels). NSAIDs and other medications that affect the adrenal glands should be used cautiously. Always provide your veterinarian with a complete list of all medications and supplements your dog is receiving.

Is trilostane safe for long-term use?

Yes, trilostane has been used safely in dogs for many years with consistent monitoring. The key to long-term safety is regular ACTH stimulation testing and bloodwork to catch any dose-related complications early. Some dogs remain on trilostane for 5+ years without significant issues. According to the AVMA, the standard of care for canine Cushing's disease involves ongoing veterinary supervision throughout the treatment period.

Which breeds are most prone to Cushing's disease?

Poodles (especially Miniature and Toy varieties), Dachshunds, Small Terriers (including Yorkshire Terriers, Boston Terriers, and Cairn Terriers), Beagles, and Cocker Spaniels are overrepresented in Cushing's disease cases. However, any breed can develop the condition, particularly in the 7–12 year age range.

Can Cushing's disease be prevented?

There is no known way to prevent naturally occurring Cushing's disease — it is caused by tumor growth in the pituitary or adrenal glands, and there are no identified environmental or dietary risk factors to avoid. However, iatrogenic Cushing's (caused by long-term steroid use) can be minimized by using the lowest effective dose of corticosteroids for the shortest duration necessary, under veterinary supervision. Regular wellness exams for senior dogs (every 6 months) improve the chances of early detection.

What is the life expectancy of a dog with Cushing's disease?

With proper trilostane treatment and monitoring, dogs with pituitary-dependent Cushing's disease have a median survival time of approximately 2–2.5 years from diagnosis, though many live 3–5 years or longer. The disease itself is rarely the direct cause of death — most dogs eventually succumb to other age-related conditions. Dogs with adrenal tumors that are successfully removed surgically may have a normal remaining lifespan if the tumor was benign.