Transdermal fentanyl: pharmacokinetics and preliminary clinical evaluation

A new transdermal drug-delivery system that administers the synthetic opioid fentanyl through intact skin was evaluated for 24 hours postoperatively in eight patients who had undergone orthopedic surgery. Plasma samples were obtained over a 72-hour period for pharmacokinetic analysis in five patients. The patients were also evaluated intensively for adequacy of analgesia, frequency of nausea and sedation, and occurrence of ventilatory depression. A median lag time of 2.25 hours after application of the transdermal system was observed before the appearance of fentanyl in the blood. Median peak concentration and time to peak were 1.0 ng/ml and 22 hours, respectively. The apparent elimination of fentanyl after transdermal administration is prolonged relative to previously reported values. Absorption analysis indicates zero-order fentanyl administration, and in addition, suggests deposition of drug in an epidermal site, with the resultant prolonged absorption process giving the appearance of slow elimination. No significant toxicities were observed. Four patients required no additional analgesia. No consistent correlations among fentanyl concentration and any clinical values were observed. Transdermal administration of fentanyl appears to be a viable alternative to conventional routes of narcotic administration and warrants further study.