Fentanyl transdermal system is a transdermal system providing continuous systemic delivery of fentanyl, a potent opioid analgesic, for 72 hours. The chemical name is N-Phenyl-N-(1-(2-phenylethyl)-4-piperidinyl) propanamide. The structural formula is:
The molecular weight of fentanyl base is 336.5, and the molecular formula is C22H28N2O. The n-octanol:water partition coefficient is 860:1. The pKa is 8.4.
The amount of fentanyl released from each system per hour is proportional to the surface area (25 mcg/hr per 7.8 cm2). The composition per unit area of all system sizes is identical.
* Nominal delivery rate per hour
Fentanyl transdermal system is a rectangular transparent unit comprising a protective liner and four functional layers. Proceeding from the outer surface toward the surface adhering to skin, these layers are:
- a backing layer of PET foil;
- a drug-containing layer of fentanyl and dipropylene glycol with hydroxypropyl cellulose;
- an ethylene vinyl-acetate copolymer membrane that controls the rate of fentanyl delivery to the skin surface; and
- a silicone adhesive. Before use, a protective liner covering the adhesive layer is removed and discarded.