Buprenorphine-induced changes in mu-opioid receptor availability in male heroin-dependent volunteers: A preliminary study

A principle of opioid pharmacotherapy is that high medication doses should occupy fractionally more opioid receptors that mediate heroin effects. In t his preliminary study we examined in vivo mu opioid receptor (mu OR) bindin g in three healthy opioid-dependent volunteers during maintenance on 2 and 16 mg sublingual buprenorphine (BUP) liquid, and after detoxification (0 mg ) under double-blind, placebo-controlled conditions, and once in matched co ntrols. Binding measures were obtained with the mu OR-selective radioligand [C-11]carfentanil (CFN) and PET 4 hrs after BUP administration. BUP induce d dose-dependent reductions in mu OR availability, 36-50% at 2 mg and 79-95 % at 16 mg relative to placebo. Heroin abusers also had greater mu OR bindi ng potential in the inferofrontal cortex and anterior cingulate regions dur ing placebo, compared to matched controls. Further studies are warranted to examine the relationship of mu OR availability with BUP therapeutic action s, and the clinical implications of increased mu OR binding during withdraw al. (C) 2000 American College of Neuropsychopharmacology. Published by Elsevier Science Inc. All rights reserved.