Pharmacokinetics, safety, and tolerability of ascending doses of sublingual fentanyl, with and without naltrexone, in Japanese subjects.

This open-label, nonrandomized study assessed single and repeat ascending doses of a new sublingual fentanyl (SLF) formulation in 48 healthy Japanese opiate-naïve subjects (47 completed). Subjects received single-dose SLF 100, 200, 400, or 800 µg followed by 13 doses 6 hourly, at their dose level. Subjects taking repeat-dose 400 and 800 µg were pretreated with naltrexone in order to block opiate-receptor-mediated effects on respiration, monitored by pulse oximetry and transcutaneous pco(2).