Fentanyl Formulations in the Management of Pain: An Update.

Fentanyl is a synthetic, highly selective opioid with many desirable physicochemical properties, including a high lipophilicity and predictable pharmacokinetics. These properties have an established record in the management of pain in a variety of settings, particularly acute pain and breakthrough cancer pain. Fentanyl was initially developed for parenteral use; however, this is invasive and impractical in the outpatient setting. Unfortunately, the high first-pass metabolism of fentanyl makes oral formulations unfeasible. However, its high lipophilicity allows fentanyl to be absorbed via a number of other routes. Thus new formulations were designed to allow non-invasive methods of administration. Transmucosal and transdermal fentanyl formulations are well established, and have proven useful in the settings of breakthrough cancer pain, emergencies and in the paediatric population. The iontophoretic transdermal system was developed to provide a needle-free system of delivering bolus doses of fentanyl on demand, a novel way of delivering patient-controlled opioid analgesia. Transpulmonary administration of fentanyl remains experimental. The aim of this review is to provide an update on current non-parenteral fentanyl formulations, with attention to their particular pharmacokinetics and features relevant to clinical use in pain management.