When to Stop Vetoryl (trilostane)

Most dogs with Cushing’s disease are treated with Vetoryl. The active ingredient in Vetoryl is an enzyme inhibitor called trilostane, which reduces the production of cortisol by the adrenal glands. When dogs are given an appropriate dose of medication, cortisol is reduced to a healthy level. If the dose is too high or the dog becomes too sensitive to Vetoryl over time, cortisol can fall dangerously low.

Because cortisol is needed to survive, too little of it can rapidly lead to a life-threatening emergency called an Addisonian crisis. To prevent this, it’s important to pause the medication and seek veterinary care as soon as possible if your dog exhibits any signs of cortisol insufficiency, such as lack of appetite, vomiting, diarrhea, collapse, or shaking. As a next step, your veterinarian will conduct an ACTH stim test or Pre-Vetoryl Cortisol test to check cortisol levels. Vetoryl should be stopped and potentially restarted at a lower dose in the following scenarios:

(1) if a Pre-Vetoryl Cortisol test shows that cortisol is below 1.5 ug/dL (41.37 nmol), or

(2) if an ACTH stim test shows that post-ACTH cortisol is below 1.45 ug/dL (40 nmol). Note: some veterinarians use a cutoff of 2.0 ug/dL.

In these circumstances, Vetoryl should not be given to the dog again until (1) at least 7 days have gone by, (2) side effects subside and the primary Cushing’s symptoms that the dog had prior to starting Vetoryl return, and (3) testing shows that cortisol levels have returned to normal. Once all of this happens, it’s normally safe to restart the medication at a lower dose.

Please note, it can sometimes take much longer than 7 days for cortisol levels to rise again. If your dog doesn’t appear to be getting better or has worsening side effects after withdrawing Vetoryl, steroids and IV fluids might be needed to revive the adrenal glands.

Remember: you are your dog’s best advocate.