5.2.2. Transdermal Systems

In this type of system, nitroglycerin and lactose are triturated in silicone fluid which is then encapsulated in a thin membrane of ellipsoid shape. The reservoir of the drug layer is introduced in between the metallic plastic laminate (backing sheet) which is impermeable and ethylene-vinyl acetate copolymer porous membrane which is the rate controlling membrane. This is formulated by the injection molding process and a thin layer of adhesive (silicone) is again coated on the permeable drug membrane for the immediate contact of the drug-releasing membrane with the skin's surface to be maintained and achieved (Figure 13). Nitroglycerin (0.5 mg/cm2)/day is delivered transdermally for treating angina [132]. Other examples are Estraderm-controlled delivery of estradiol for 3–4 days to relieve postmenopausal syndrome and osteoporosis [133], Duragesic-controlled delivery of fentanyl for 72 h to relieve chronic pain [134] and Androderm-controlled delivery of testosterone(24 h) used as an additional therapy for patients with testosterone deficiency [135].

**Figure 13.** Diagrammatic representation of membrane permeation-controlled system in which the drug reservoir is sandwiched between the membrane layers and the adhesive layers facing the skin's surface (adapted from [134]).
