**3.3 Transdermal route**

Topically given pharmaceuticals in the form of patches that, when placed to the skin distributes the drug through the skin at a predetermined and controlled pace are referred to as transdermal drug delivery systems. Transdermal patches distribute drugs via the skin in a controlled and predefined manner, resulting in increased therapeutic efficacy and fewer side effects. The medications must be able to permeate the skin and reach the target site to be effective in a transdermal drug delivery system. When compared to the oral route, TDDS improves patient compliance and reduces load [6].

Transdermal delivery of drugs through the skin to the systemic circulation is a useful methodology of administration for a variety of clinical indications. Transdermal delivery systems are available for scopolamine (hyoscine) for motion sickness, clonidine and nitroglycerin for cardiovascular disease, fentanyl for chronic pain, nicotine for cessation of smoking, oestradiol (alone or in combination with levonorgestrel or norethisterone) for hormone replacement, and testosterone for hypogonadism [22].

Some of the possible benefits of transdermal drug delivery include controlled absorption, more consistent plasma levels, increased bioavailability, decreased adverse effects, painless and uncomplicated application, and the flexibility of discontinuing drug administration by simply removing the patch from the skin. Padula et al. reported a novel drug delivery system consisting of a water-based, vapour permeable membrane for cutaneous and/or transdermal distribution. The goal of this study was to control the administration of the model drug lidocaine hydrochloride through rabbit ear skin using a transdermal film. On lidocaine transport over the skin, the effects of drug loading, film-forming polymer type and content, adhesive and plasticiser were studied [23]. Aside from that, Ammar HO et al. (2013) developed and tested a transdermal ketorolac film-forming polymeric solution for pain treatment employing Eudragits® RLPO, RSPO, and E100, as well as polyvinyl pyrrolidone K30 dissolved in ethanol as film-forming solutions. An improved transdermal ketorolac formulation has shown a significant potential to provide a rapid and enhanced analgesic impact, which is a critical requirement in pain treatment [24].
