The transdermal administration of fentanyl in the treatment of postoperative pain: pharmacokinetics and pharmacodynamic effects.

A transdermal formulation of fentanyl (TTS-fentanyl, Alza Corp., Palo Alto, CA) was evaluated in 13 surgical patients after an abdominal operation. An intraoperative dose of fentanyl (100-200 micrograms i.v.) was administered at the same time as the TTS-fentanyl systems (50-125 micrograms/h) were applied to the antero-lateral chest wall. The TTS-fentanyl systems remained in situ for 24 h and were then removed and a second lot of systems were applied to the contra-lateral chest wall. There was a mean (S.D.) delay time of 12.7 (9.6) h before minimum effective blood fentanyl concentrations (MEC) were obtained from the systems and pseudo-steady state was reached between 36 and 48 h. There was a decay time of 16.1 (7.1) h after the systems were removed for the blood fentanyl concentration to decrease to less than the mean MEC for the control of postoperative pain. There was marked variability between patients in the actual hourly fentanyl dose rate determined from the residual amount of fentanyl remaining in the system and the duration of application. Significantly more supplementary pethidine was administered for inadequate postoperative analgesia between 0 and 12 h compared to the 12-24, 24-36 and 36-48 h periods; this was consistent with the observed delay time. Three patients required a reduction in the hourly fentanyl dose rate because of bradypnoea while 1 patient required an increase in dose because of inadequate pain relief. Nausea was the most frequently reported side effect (85% of patients) while bradypnoea, drowsiness, unpleasant dreams and headache were also reported. These effects were due to the combined effects of a sustained blood fentanyl concentration and the intermittent supplementary pethidine doses. Side effects due to the topical formulation were transient and included erythema (8 patients) and a minor rash (2 patients) in the area occluded by the systems. The TTS-fentanyl systems provided a significant contribution to postoperative pain control but, at the TTS dose rates used, supplementary doses of pethidine were required by all patients probably to control 'incident' pain.