Pimozide: The Opiate Antagonist Hypothesis and Use in Delusions of Parasitosis

Introduction: Pimozide, a neuroleptic agent frequently used in the treatment of delusions of parasitosis, has been thought to have a better therapeutic efficacy for delusions of parasitosis than other antipsychotic agents because of its dual effect of blocking opiate as well as dopamine transmission. If so, this may present a problem in patients who are dependent on opiates, who would undergo withdrawal when given a strong opiate antagonist such as naloxone. Methods and Results: A literature search was conducted and evidence was found to alleviate these fears that pimozide would precipitate opiate withdrawal. Although no reports of human studies were found, several studies have shown that withdrawal is not observed when giving pimozide to opiatedependent animals. Moreover, the bases for the mechanism of pimozide as an opiate antagonist and for the role of opiate neurotransmission in delusions of parasitosis were found to be still controversial.