Medicines that are administered by oral and parenteral routes still dominate the technology by which drugs are delivered to the patients for treating diseases and ailments. However one form of delivery system where drugs are delivered smoothly through the pores of skin into systemic circulation, known as transdermal drug delivery (TDD) has provided an attractive alternative to oral delivery of drugs and is poised to provide an alternative to hypodermic injection too. These delivery systems are Band Aid-like strips and are broadly known as transdermal patches or simply a TD patch.
The patients have only to attach a patch to a suitable and convenient part of the body (upper arm, chest, behind ear, trunk etc.) and do nothing except reapply it every predetermined time. Besides, you don’t need a doctor or a nurse to put the patches on you. The first transdermal patch, a three-day patch that delivers scopolamine to treat nausea and vomiting associated with motion sickness—was approved for use in the United States way back in the year 1979. This TD patch provided a novel form of drug delivery and was a therapeutic breakthrough. Today, there are more than 20 drug molecules as transdermal products containing drug(s) for chronic pain management, contraception, hormone replacement, and tobacco cessation. Some of the molecules are scopolamine, nitroglycerin, estradiol, clonidine, nicotine, testosterone, lidocaine, fentanyl, norethidrone acetate and oxybutymin The transdermal patch marked the beginning of the advanced era of non-invasive systemic drug delivery.
The transdermal patch or the device which is the cornerstone of this innovative technology comprises five discrete layers. The outermost layer is a backing layer of polyester film, followed by a drug reservoir which is a suspension or solution of a drug in a suitable vehicle. The third layer consists of micro-porous membrane of varying pore size that controls the release of the drug from the system to the skin surface. The fourth is a thin, adhesive membrane, which is used to fix the patch to the skin. And the fifth and lowermost is the protective peel strip.
As soon as the patch is attached to the skin, drug diffuses out of the system through the skin into blood circulation by percutaneous absorption. The amount of the drug to be released can be adjusted by controlling the membrane or polymer matrix complex. The size of the patch is consistent with the type of the drug and the dose required. For example, a dose of 0.5 mg scopolamine for three days requires a patch of 2.5 sq. cm. in area.
The transdermal patch offers a number of advantages scores over oral medications that include the avoidance of first pass metabolism & GIT degradation, allows for the administration of drugs with narrow therapeutic window, can reduce frequency of dose for relatively short acting drugs, eliminates the need for hypodermic injections, and simple application. The drug needs only once in 2/3 days or even a week from a patch instead of several times a day.
The major limitation of transdermal patch is the low skin permeability of most of the drugs. Only relatively low dose drug are suitable for (first-generation) transdermal delivery. Nonetheless many drugs have been developed with skin penetration enhancer (categorize as second generation) and third generation tragedy targets layer of stratum corneum to enhance penetration of drug. These advances in third generation transdermal delivery, particularly with microneedles, are enabling a wider range of drugs to be delivered through the skin.
Considering the recent advancements and all those discussed, time is not far away when patients need not take drugs orally or through injections, simply to attach a TD patch to a convenient part of body instead.