Fentanyl-blocking effects of extended-release naltrexone in humans: Three case reports.

Despite the contribution of the µ-agonist fentanyl to the United States's opiate overdose epidemic, no human studies specifically address the ability of extended-release preparations of the opiate antagonist naltrexone (NTX) to block fentanyl's life-threatening µ-agonist-mediated respiratory depression. This paper presents three case histories of clinically necessary opiate challenges in opiate-abusing patients implanted with extended-release NTX (ER-NTX). It also reviews the sparse literature and is the first evidence that antagonist blood levels from ER-NTX preparations can completely block the lethal µ-agonist effects of at least 1,000 mcg of intravenous fentanyl.