Pharmacokinetics of transdermal drug delivery

The pharmacokinetics of drug delivery from transdermal controlled-release devices consisting of (a) a membrane plus a reservoir or (b) a monolithic slab are examined. For the period when the devices act as if the drug reservoir were infinite, simple relationships for the steady-state slope and time lag are derived and studied. An analysis of the time region when depletion of the finite dose is obtained is used to estimate the useful device lifetime. Applications to patch design are discussed.