Medication Delivery: Transdermal Patches
According to the American Pharmaceutical Association, about 46 percent of Americans use one or more prescription drugs. Drugs are commonly taken in the form of a pill. But they can also be injected, inhaled, or applied topically (i.e., a cream or gel). Another route of medication administration is the transdermal (through the skin) patch. Drug patches look like oversized bandages. They are designed to deliver medications through the skin.
There are several different kinds of patch systems. In a single layer patch, the drug is incorporated into the middle layer – an adhesive which holds the patch on the skin. The top or outermost layer is an impermeable cover that keeps the drug inside and reduces moisture loss from the skin. The innermost layer is a liner or membrane that sits on the skin and holds the drug in the patch from the other side. A multilayer drug patch contains a backing, one or more additional layers of the drug-containing adhesive, and the liner. A special membrane may separate the layers of adhesive to control delivery of the medication. Reservoir patches contain a tiny compartment with a liquid drug solution or suspension. Matrix patches contain a semisolid matrix with a drug solution or suspension.
Transdermal patches must be placed on areas where they make direct contact with the skin (i.e., less hairy areas of the body). For most people that means the upper arms, chest, or shoulders (the lower body is usually avoided because some people have problems with circulation in the lower torso). Once applied to the skin, the patch slowly releases the drug. The medication passes through the skin and is absorbed directly into the bloodstream.
Use/Advantages of Drug Patches
Several different medications are available in patch form. Some of them include: scopolamine (for motion sickness), nicotine (to stop smoking), estradiol (for symptoms of menopause and birth control), clonidine (for high blood pressure), nitroglycerine (for angina, or chest pain), lidocaine (an anesthetic), fentanyl (to control pain), and testosterone (hormone replacement for men). Researchers are also developing patch forms of medication to treat other conditions, such as Parkinson’s disease, generalized anxiety disorder, osteoporosis, diabetes, Alzheimer’s disease, and attention deficit disorder.
There are several advantages to transdermal patches. Oral medications must pass through the gastrointestinal tract, then into the liver. Here, foreign substances, such as drugs, are broken down , lowering their effectiveness. With the patch, drugs enter the bloodstream directly, reducing the risk of gastrointestinal side effects and bypassing breakdown by the liver. (Injectable medications also bypass the digestive system, but patients are usually reluctant to continually give themselves injections.) Some drugs must be taken several times a day. That schedule increases the chance of noncompliance because patients can forget to take a dose or find it too inconvenient. Drug patches are more convenient because they usually only need to be placed once a day or every few days. In addition, oral drugs lead to a fluctuation in active ingredients, with more of the drug in the body soon after taking a dose and less as the time for the next dose nears. With the patch, there is a constant, slow release of medication into the bloodstream.
Few people have difficulties with the patch (some develop skin irritation from the adhesive). Side effects of transdermal medications are the same as the oral forms. So if a patient has no problem with an oral drug, the patch shouldn’t cause side effects either. And if a patient does experience a problem, the patch can simply be removed, reversing the effects. For oral or injectable medications, side effects can’t be stopped until the drug has cleared the body.
For general information about pharmaceuticals talk with your pharmacist, or visit one of the following sites:
American Pharmaceutical Association, http://www.pharmacyandyou.org
Pharmaceutical Research and Manufacturers of America, http://www.phrma.org