|English: 2D structure of fentanyl (Photo credit: Wikipedia)|
Fact or Fiction From Medscape:
Q: Is it true that fentanyl patches infuse more quickly in patients with very little subcutaneous fat?
A: No. The amount of fentanyl absorbed is proportional to the surface area of the patch. The absorption rate does not vary to any clinically significant extent between the chest, abdomen, and thigh. Fentanyl is released from the patch into top layers of the skin (stratum corneum and epidermis), and it accumulates within these layers to form a depot. The drug is released slowly into the systemic circulation via small blood vessels within the dermis. Fat tissue should not impair release, as the drug is released directly from the skin into the blood supply.[2,5]
Furthermore, fentanyl exhibits wide tissue distribution to the lungs, kidneys, heart, spleen, brain, muscles, and body fat -- indicating a high extravascular volume of distribution (3-8 L/kg). It takes about 6 days to reach steady-state plasma concentrations after initiating fentanyl patch therapy.
- Muijsers BBR, Wagstaff AJ. Transdermal fentanyl: an updated review of its pharmacological properties and therapeutic efficacy in chronic cancer pain control. Drugs. 2001;61:2289-2307. Abstract