Principles of the design and operation of generic osmotic pumps for the delivery of semisolid or liquid drug formulations

Abstract

Miniature osmotic delivery systems were constructed and tested in various environments according to the design criteria described in the present paper. These devices, when activated by water, can deliver a variety of solutions or suspensions at zero-order rates for periods of hours up to several weeks. The osmotic pumps consist of a cylindrical reservoir for the fluid, surrounded by a layer of an osmotic driving agent which, in turn, is encapsulated by a semipermeable membrane. The reservoir material is chemically inert to most aqueous drug formulations, dilute acids, bases, and alcohols. The outer housing of the pump, which is the membrane, is highly compatible with tissues when the pumps are implanted in animals. Typically, the miniature pumps have a total volume of approximately 0.6 ml, and an internal effective volume of approximately 0.2 ml. The delivery rate can be varied from 0.1 to 3 μl/hr. Devices of this type have been tested successfully as implants in mice for anticancer drug research, in endocrine studies, and in narcotic-drug evaluations. The time course of the pumping ratein vivo is accurately specified by thein vitro pumping rate under conditions that are isotonic and isothermal to extracellular fluid.