Time to reach Analgesic Levels.

It takes 6-12 hours after the patch has been applied to reach analgesic levels.

It may be necessary to cover this period with the appropriate dose of normal release morphine.

Time to reach Steady State Plasma Levels.

It will take 12 - 24 hours to reach steady state* plasma levels of fentanyl.

*‘Steady State occurs when the dose that is metabolised and excreted during each dosage interval, is an amount equal to the dose administered at the start of the interval’ (References).

Because of this any increase in the dose of fentanyl should normally not be made before 48-72 hours have elapsed.

Remember the appropriate dose of normal release morphine for breakthrough pain - see conversion tools.