Interestingly, some dogs in the study had clinical evidence of illness (anorexia, lethargy, vomiting) despite cortisol concentrations that may not be as low as expected. This may be because trilostane may more effectively inhibit mineralocorticoid synthesis in this population of dogs while cortisol concentrations may be less affected.

Overall, five of the 47 dogs appeared to have adverse reactions to trilostane, but unrelated conditions may have resulted in the illnesses. Four of the five dogs with adverse effects were receiving doses well below the manufacturer's suggested dosing, a fact noted even in those dogs that were receiving medication three times a day. Additionally, these effects may occur at any point during treatment as seen in those dogs that developed problems at two months, six months, and one year after therapy was initiated.

The author of the study recommends that the goal of therapy should continue to be a post-ACTH cortisol concentration ≤ 5.5 µg/dl and urine specific gravity > 1.020 but that owner observations regarding treatment response also be considered. Trilostane appears to be effective at lower doses than those recommended in the literature and by the manufacturer, so a lower-dose protocol may successfully achieve a therapeutic response while decreasing the risk of adverse events. Additionally, the need to increase dosing frequency should be considered in those dogs that have an appropriate biochemical response but are still exhibiting clinical signs.

This "Hot Literature" update was provided by Jennifer L. Garcia, DVM, DACVIM, a veterinary internal medicine consultant in Houston, Texas.