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Information about the previous Durogesic Transdermal Patch

Patch technology e.g how Durogesic Reservoir patches work

Each Durogesic patch contains fentanyl, which is an opioid. The sticky side of each patch is made of a semi-permeable membrane, which allows the medication to pass through it at a controlled rate.

When the patch is applied to the skin, the fentanyl inside the patch slowly moves through this membrane and becomes absorbed by the skin underneath.

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 36-48 hours.

diagram of fentanyl patch activating on skin

Twycross has described the difference between morphine and fentanyl diagrammatically as follows:

diagram of Morphine and Fentanyl distribution from Vascular to Central nervous system

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.