Naltrexone-induced pruritus in a dog with tail-chasing behavior.

Naltrexone, an opioid antagonist recently advocated for the control of stereotypic behavioral patterns in horses and dogs, induced an intense dose-related pruritic reaction in a dog with tail-chasing and self-mutilating behavior. Used in human beings primarily as an adjunct in the treatment of opioid abusers, naltrexone's adverse effects include dermatologic signs, such as alopecia and pruritus, observed in < 1% of human patients. In contrast to previously reported findings, naltrexone treatment was of limited benefit to the dog of this report. During administration of the drug, stereotypic patterns were reduced but did not disappear. Although naltrexone may be effective in controlling certain obsessive-compulsive disorders, its inconsistent therapeutic value, prohibitive cost to pet owners, and side effects such as the pruritus observed in the dog of this report may restrict use of this drug.