This study evaluated the single-dose and steady-state pharmacokinetics of fentanyl buccal tablet 400 microg in healthy adult volunteers. After receiving naltrexone 50 mg to block opioid receptor-mediated effects of fentanyl, subjects received fentanyl buccal tablet 400 microg on day 1, then every 6 hours from day 4 to day 9 (21 doses). Naltrexone 50 mg was administered every 12 hours throughout the study. Plasma fentanyl concentrations were determined for 72 hours after administration of fentanyl buccal tablet 400 microg on day 1 and the last dose of fentanyl buccal tablet 400 microg on day 9. Following single- and multiple-dose administration of fentanyl buccal tablet, the median time to maximum concentration (tmax) was 52.2 and 49.8 minutes, respectively. Peak plasma concentration of fentanyl (Cmax) was 0.88 ng/mL for the single-dose regimen and 1.77 ng/mL for the multiple-dose regimen. Steady state was reached within 5 days, consistent with the observed median half-life of approximately 22 hours following multiple doses. Observed accumulation of fentanyl after multiple doses of fentanyl buccal tablet was slightly greater than would be expected based on the single-dose data. This was attributed to the redistribution of fentanyl from a deep tissue compartment into the plasma. This study indicates that fentanyl buccal tablet has predictable pharmacokinetics following multiple-dose administration.