Abstract

A transdermal drug delivery system useful for the controlled, for example zero order release of one or more drugs to a selected skin area of a user, which system comprises an impervious backing sheet and a face membrane, the backing sheet and membrane secured together to form an intermediate reservoir. The face membrane is a macroporous membrane which has pores of sufficient size to avoid any rate control of the drug to be transdermally delivered to the user. The reservoir contains a viscous liquid base material selected to exude from the membrane to form a film and to occlude the skin of the user to force hydration of the stratum corneum with water from the lower layers of the epidermis of the user and a plurality of solid microparticles generally uniformly dispersed and suspended in the liquid base material. The microparticles containing an effective therapeutic amount of the drug for transdermal delivery, such as the contraceptive steroid. In use the liquid base material exuded from the macroporous membrane face forms a thermodynamically stable thin film layer in an intimate contact with the skin, while the drug is released from the microparticles into the base material and transdermally into the user.