What is Transdermal Drug Delivery?

C. Stoliecki

There are several different methods of administering drugs into the body. These include intravenous methods, oral methods and epidural methods. One method, known as transdermal drug delivery, applies the drug directly to the skin where it is absorbed into the body. There are several mediums that have been used to administer drugs via the unbroken skin. These include plasters, various ointments and, most commonly, patches.

Medicated patches deliver drugs into the bloodstream over a long period time in small doses.
Medicated patches deliver drugs into the bloodstream over a long period time in small doses.

Plasters, or thick pastes containing the drug to be administered, have been used throughout history to treat various medical conditions. One example is known as mustard plaster. Mustard plaster was prepared with ground mustard seeds and water and applied to the chest of a patient suffering from congestion. It was most often spread on a piece of flannel and held in place with a cloth wrap.

Ointments are another medium for transdermal drug delivery. For instance, historically, mercurial ointment was made from liquid mercury and mercuric soap and lard. The resulting ointment was used as a treatment for syphilis, as well other ailments.

Typically, contemporary transdermal drug delivery begins with what is commonly referred to as a patch. These devices contain a small pad that contains the desired drug. Patches are applied to the skin and held in place by a safe adhesive so that they can continuously deliver medication over a specified time period. This method has been successfully used to deliver nitroglycerin, nicotine, and hormones administered for contraceptive purposes.

There are several advantages to administering drugs transdermally. First, the method of delivery is non-invasive, which is much less traumatic to the patient than other forms of drug delivery such as intravenous administration. Also, it can be effective in assuring that a patient receives a full dosage of drugs in cases that where there is a high likelihood that the patient will forget a dose. This is common in instances where patients are required to take a many pills throughout the day.

Administering drugs transdermally is also advantageous in that the drugs enter the circulatory system without having to pass through the digestive tract. Many drugs are associated with causing digestive upset in a majority of patients and these uncomfortable symptoms can often be avoided with transdermal drug delivery. These forms of drug delivery are also beneficial in patients experiencing dysphagia, a medical condition that causes difficulty and pain upon swallowing, which makes it difficult for them to swallow pills.

Despite the advantages, there are difficulties associated with administering medication through the skin. The natural function of the skin is to act as a protective barrier, so it is often the case that drugs are not chemically suited to penetrating it. Researchers have discovered several things that can help to solve this problem such as applying chemicals to enhance the ability of certain drugs to be absorbed into the skin.

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