Transdermal fentanyl therapy: system design, pharmacokinetics and efficacy

The transdermal route of drug delivery has been used for the effective administration of therapeutic agents for more than a decade. The most important consideration in selecting a drug for transdermal delivery is the potential for improving therapeutic efficacy. The development of a transdermal fentanyl system provided an opportunity to add fentanyl to the armamentarium of strong opioids available for the treatment of cancer pain. The transdermal route of administration has advantages over both the oral and parenteral routes. In addition, patient and caregiver factors allow improved acceptance of and compliance to strong opioids and therefore improved analgesic outcome. Four transdermal fentanyl systems are available, providing delivery rates ranging from 25-100 micrograms/h; higher rates can be achieved by multiple system application. The system releases fentanyl continuously for 3 days when applied to the skin. Concentrations of fentanyl in the blood are measurable within a few hours of system application. Fentanyl serum concentrations increase gradually, generally levelling off after 12-24 h and remaining relatively constant for the remainder of the 3-day period. Steady state serum concentrations are reached by the second application. Clinical trials have established the efficacy and safety of transdermal fentanyl for the treatment of cancer pain. Transdermal fentanyl is not licensed for the treatment of acute pain, e.g. postoperative pain, and should not be prescribed for this purpose.