Nalrexone Facilitated Discontinuation of Buprenorphine

The efficacy of buprenorphine as a long-term agonist treatment has been offset by the emergence of intolerable withdrawal phenomena in a subset of individuals on chronic maintenance who attempt to discontinue the medication. Efforts are needed to better understand these challenges encountered with buprenorphine, as well as to develop interventions to facilitate medication discontinuation. Emerging evidence suggests that these difficulties may be related to the unique effects of buprenorphine on sites other than mu-opioid receptors, such as kappa-opioid receptors. Kappa-opioid agonism produces aversive, dysphoric-like effects, and can also increase the likelihood of reinstatement to drug use through stress-mediated mechanisms. Some of the discomfort observed during drug taper may therefore be due to the attenuation or loss of kappa-opioid antagonism afforded by buprenorphine, as well as to rebound kappa-opioid activation. Naltrexone represents a promising candidate for extending kappa blockade and therefore for facilitating discontinuation attempts. Naltrexone and its active metabolite 6-Beta-naltrexol are competitive antagonists at the mu and kappa receptors, and to a lesser extent at the delta receptor. Naltrexone and buprenorphine have comparable affinity for the mu-opioid receptor and thus buprenorphine is displaced by naltrexone more gradually than are other opioids with less affinity; a careful titration of naltrexone is less likely, therefore, to precipitate severe withdrawal states in individuals coming off buprenorphine, and the two have been combined to good effect in other settings. The purpose of this study is therefore to investigate the feasibility of naltrexone augmentation on discontinuing buprenorphine in eligible patients on long-term maintenance.