WE MOVE News...Health Literacy: Understanding the Use of Patch-based Drugs
 

WE MOVE News
Subject: Health Literacy: Understanding the Use of Patch-based Drugs

Date: 2/10/2007
http://www.wemove.org/stayconnected/article.asp?ID=921

When most people think of "the patch," what comes to mind is the nicotine patch that is used to help people stop smoking. However, pharmaceutical or drug companies have also developed other patch applications of drugs such as hormones, scopolamine to treat motion sickness, nitroglycerine for chest pain, lidocaine and fentanyl for pain control, methylphenidate to treat attention-deficit/hyperactivity disorder, and others.

The "patch" is a form of transdermal drug delivery. Patches that are used in transdermal drug delivery are made up of several thin, flexible layers, including a liner, an adhesive, a membrane, and a backing. The liner is part of the packaging and is removed when you apply the patch to your skin, the adhesive allows the patch to stick to your skin, the membrane controls how fast the drug actually gets into your blood stream, and the backing protects the drug from contamination while you wear the patch. Patches contain the drug in either a reservoir, which contains the drug in a separate layer, or a matrix, which combines the drug with the adhesive.

Sometimes things that seem easy or simple may actually be complex and complicated. This is true for the patch. For example, most substances are made up of molecules that are too large to be able to get through your body's primary defense mechanism against germs and other harmful substances-your skin. Simply applying a pill to your skin and covering it with a bandage would not allow the drug to be absorbed. Instead the medicine used in transdermal or "across-the-skin" drug delivery is added to a substance or technique that makes the skin ready to receive the drug. The drug can then get through or penetrate the skin and is absorbed into your bloodstream. However, because of limits in technology, not all drugs can be delivered in this way.

Transdermal drug delivery has several advantages over pills that are taken by mouth. When drugs are taken by mouth, it is difficult to maintain a constant level or steady state of the drug in your bloodstream. Transdermally delivered drugs are released slowly over a specific period of time. Depending on the drug, this time can vary from a few hours to a few days or even longer, at which time the old patch is replaced with a new patch. When you put on the new patch, the medicine is maintained at the same steady state in your bloodstream. Another advantage is that, if side effects develop, these effects of the drug stop within a brief period of time after you remove the patch. With medicines that you take by mouth, the side effects continue as long as the drug remains in your system. A third advantage is that transdermal drug delivery avoids the passage of the drug through your liver and gastrointestinal tract. When you take medication by mouth, the liver destroys many drugs. In addition, what you eat and drink and when you eat and drink in relationship to when you take your medicine affects the amount of the drug that is absorbed into your bloodstream. For example, if you eat a meal that is high in protein and then take levodopa, you won't absorb as much levodopa through your gastrointestinal tract as if you had taken your medicine an hour or more after eating. Finally, transdermal drug delivery is useful if you have difficulty swallowing or can't take medicines by mouth. For example, if you are having an operation, you can't take medicines by mouth, so the doctor could administer your medication by applying a patch while you are having the operation.

Several medicines that are of particular interest to people with movement disorders are now being developed for transdermal delivery. These include rotigotine, a new dopamine agonist, that is being studied for use in people with Parkinson disease and restless legs syndrome. Rotigotine is available for sale in Europe but is not yet approved in the United States. Lisuride, another dopamine agonist, is currently available in pill form for the treatment of Parkinson disease and is being studied in a patch form. Selegiline is approved in the pill form for the treatment of Parkinson disease and recently was approved in a patch form for the treatment of depression.