This article was based on research Wendy did during Summer 2000, when she participated in the Center for Polymer Interfaces and Macromolecular Assemblies Summer Undergraduate Research Experience at Stanford University. For her project, she investigated the adhesive properties of transdermal drug delivery systems.

The teenage years are a susceptible time for experimentation, when peer pressure to look cool and light up begins an addiction that is difficult to overcome. Fortunately, societal pressures to quit smoking are more overwhelming now than ever before. Increasing awareness of the hazardous health effects of second-hand smoke on nonsmokers has been a cause for concern in the nonsmoking community; consequently, businesses have been pressured to take action. Airlines, restaurants, and workplaces either limit smoking to designated smoking areas or ban it entirely. As much pressure as there is to quit, it is just not that easy.

According to the American Cancer Society, of the 17 million Americans that try quitting each year, only 1.3 million actually succeed.³ The rest cannot escape the grasp of nicotine - the powerful ingredient in cigarettes found to be addictive by the Surgeon General in 1988.³ The withdrawal effects that accompany the nicotine craving include irritability, anger, anxiety, restlessness, hunger, and the inability to concentrate. ^3,7 Normal functioning is completely disrupted; psychological, physiological, and behavioral effects are all represented by these symptoms.

There are, however, weapons available on the market to help make the battle to quit smoking easier. The newest product is the nicotine patch, which looks like a Band-Aid but is much more sophisticated. It delivers small doses of nicotine to the bloodstream, so that a constant low level of nicotine is maintained in the body.⁷ This is intended to satisfy the nicotine craving without the pleasurable "buzz" that comes from smoking. Tablets provide an addictive "buzz" since they immediately supply a high level of the drug to the bloodstream.⁴ It is both easy and tempting for patients to take more than the recommended dose of tablets, unlike nicotine patches, which give patients minimal control over their nicotine intake. Furthermore, the patch's automatic delivery of nicotine to the body permits the smoker to focus on overcoming the physical habits that go hand in hand with smoking. These include "having something in the hand or mouth, drawing smoke in and puffing it out, or reaching for a cigarette in response to a behavioral cue, such as a cup of coffee or stress."³

The nicotine patch essentially uses a transdermal drug delivery system. The main concept behind the patch is that liquids in direct contact with the skin can be absorbed to some degree.⁴ The two main delivery systems are the membrane-controlled and the matrix systems; schematics of both are shown below.⁶

The membrane-controlled system consists of four layers: the backing layer, the drug reservoir, the rate-controlling membrane, and the adhesive. The drug reservoir stores the nicotine and liquid excipients that encourage skin absorption of the drug.⁶ The drug diffuses through the membrane in uniform amounts and then passes through the adhesive before reaching the skin. The drug release rate is constant, so it must be maintained at a level below the skin's saturation limit.¹ For the matrix system, the adhesive serves the dual roles of the adhesive and drug reservoir. In this design, the drug is delivered to maintain skin saturation.¹ Hence, the drug diffusivity is dependent on the skin's absorption rate. When the drug level in the patch falls below the saturation limit, the rate of drug delivery will gradually diminish over time.

Both the membrane-controlled and the matrix systems allow nicotine to exist in the bloodstream at a small but constant level over a long period of time, unlike oral therapy which has a "peak and valley" effect.² Oral drug delivery via tablets is not sophisticated enough to provide controlled drug release; each dose quickly raises the drug concentration in the bloodstream to its maximum level and then plummets. At high concentration levels, there is a risk of harmful side effects, but at the other extreme, the concentration is so low that the patient derives no medical benefit. Hence, "it is desirable to release drugs at a constant rate, thereby maintaining drug concentration within the therapeutic range and eliminating the need for frequent dosages."⁵

Transdermal drug delivery systems hold a gold mine of promise in the medical field; nevertheless, typical of all young developments, a number of shortcomings in their performance need to be addressed. First, a smaller and less conspicuous design that still maximizes skin coverage is desired to increase comfort so that the activity of the patient is not inhibited. Second, adhesive failure occurs when the skin becomes wet or sweaty, which poses serious problems during exercise or bathing since many patch designs require 24 hour wear. The greatest shortcoming is the difficult removal of the patch, resulting in skin irritation.⁶ Consequently, research is underway to optimize the nicotine patch so that smokers have a reliable and effective aid to battle their addiction.