Passive absorption of fentanyl from the fentanyl HCl iontophoretic transdermal system

Background: The fentanyl HCl iontophoretic transdermal system (ITS) is a patient-controlled analgesic delivery system that actively administers bolus doses of fentanyl transdermally upon patient activation. Objective: To determine the amount of fentanyl absorbed from fentanyl ITS via passive absorption over a 24.5-h period. Methods: Serial blood samples for pharmacokinetic analyses were obtained from healthy adults who received fentanyl ITS for 24 h. Findings: The average absorption rate was 2.3 mu g/h. An average total of 57.4 mg fentanyl was absorbed during the study. The mean maximum observed serum fentanyl concentration was 0.06 ng/mL. Conclusions: Results indicate that the average amount of fentanyl absorbed passively or via passive delivery from fentanyl ITS is minimal. Maximum serum fentanyl concentrations fell below the range associated with analgesia and respiratory depression. The variability in fentanyl exposure was likely exaggerated by the low amounts of drug absorption resulting in overall fairly low fentanyl concentrations.