5.2.6. Nitro-Dur System

This type of system is fabricated by heating a hydrophilic polymer, glycerol, and polyvinyl alcohol and then lowering their temperature to develop a polymer gel. Nitrogylcerin and lactose are mixed and dispersed in the polymer, which is solidified at room temperature to form a medicated disc by molding technique. This is assembled into a metallic plastic laminate where the transdermal patch is developed with an adhesive rim. This patch is designed for application to the skin for continuous release of 0.5 mg/cm<sup>2</sup> for angina treatment. Poly (isobutylene) or poly (acrylate) adhesive are the polymers used in this method and this polymeric adhesive is spread by solvent casting technique over the area of the drug impermeable membrane (Figure 17) [140]. The marketed formulations are Frandol tape by Toaeiyo/Yamanouchi in Japan—isosorbide dinitrate [141]; Nitro-Dur II by Key in the United States—nitroglycerin, which replaces Nitro-Dur, a first generation patch from the market;Habitrol and Nicotrol—nicotine (smoking cessation) [142]; Minitran—nitroglycerin [143], Testoderm—testosterone (testosterone replacement therapy) [144], and Climara—estradiol (vasomotor system treatment associated with menopause) [145].

**Figure 17.** Nitro-Dur system (adapted from [140]).
