Durogesic DTrans® is bioequivalent to the familiar Durogesic fentanyl transdermal reservoir patch and has a similar pharmacokinetic profile.
The patch, illustrated below, consists of a backing layer and solid drug-in-adhesive matrix which both contains and releases the stong opioid fentanyl (in a dissolved state) while simultaneously functioning as an adhesive. Once the patch is applied to the skin, the fentanyl dissolved within the matrix is slowly absorbed by the skin underneath.
As with the reservoir fentanyl patch the fentanyl concentrates in the upper skin layers in a depot. Once the depot is formed, the fentanyl is carried by the bloodstream and because of its high lipid solubility is rapidly taken up by adipose tissue till saturation is reached then plasma levels rise to reach Steady State at about 12 hours.
Twycross has described the difference
between morphine 
and fentanyl 
diagrammatically as follows:
Distribution of equipotent doses of morphine and fentanyl in the vascular and central nervous systems based on animal data. Converting from oral or parenteral morphine to transdermal or parenteral fentanyl will result in massive decrease in opioid molecules outside the CNS. This will result in less constipation and could, in physically dependant subjects, precipitate peripherally-mediated withdrawal symptoms.
