An open-label study15 evaluating 1069 patients demonstrated that 60% of patients remained on the drug at 12 months. Efficacy was maintained throughout the 12-month study period in responding patients.

Sixteen percent of patients discontinued therapy due to adverse events, with an additional 3.8% stopping therapy due to lack of efficacy. The results of the study appear to closely resemble the author’s Bosutinib experience in clinical practice. Transdermal Drug Delivery Advances in polymer science and drug formulation have resulted in the development of transdermal medications for the treatment of a number of medical conditions, including estrogen and androgen Inhibitors,research,lifescience,medical deficiency syndromes, contraception, analgesia, smoking cessation, and OAB. In general, transdermal delivery is convenient and offers a number of advantages over oral drug therapy, including improved pharmacokinetics, a more

convenient dosing schedule, and a lower incidence of adverse events. Skin Inhibitors,research,lifescience,medical Science and Drug Absorption The skin is broadly divided into the epidermis, dermis, and subcutaneous tissue. Drugs must penetrate the relatively avascular epidermis and reach the rich capillary system located Inhibitors,research,lifescience,medical in the underlying dermis to be absorbed into the systemic circulation. Drug absorption is affected by biologic and physiochemical properties of the various skin layers, the nature of the medication, and the design of the drug delivery system.16 The stratum corneum of the epidermis is the primary rate-limiting barrier to drug absorption. Lipophilic substances transit the stratum corneum through the lipid-rich

intercellular spaces, whereas more hydrophilic molecules dissolve and diffuse through the cell cytoplasm. Absorption Inhibitors,research,lifescience,medical through the skin can be influenced by a number of factors, including radiation, solvents, exfoliative diseases, Inhibitors,research,lifescience,medical and dermal blood flow.16 Drug absorption is also influenced by the presence of cutaneous cytochrome 450 enzymes that have the potential to oxidize drugs, resulting in approximately 10% to 20% first-pass metabolism.17 The properties of the drug and its vehicle also influence skin permeation and absorption. Lipophilic drugs such as oxybutynin are better suited for transdermal delivery because of their increased solubility and ability to diffuse through the cutaneous secondly layers. Penetration enhancers increase skin permeability by interacting with intercellular lipids and/or denaturing cutaneous proteins.16 Drug delivery is a function of the type of device used to store and release the medication. Matrix patches combine the drug and rate-controlling permeation enhancer into a single layer. These systems are smaller and thinner, and drug release is controlled by diffusion through the polymeric matrix.16 In contrast, reservoir/-membrane-controlled systems contain the drug in a polymeric membrane that controls the rate at which the drug is released.