A transdermal patch is a medicated adhesive patch that is placed on the skin to deliver a time released dose of medication through the skin and into the bloodstream. The most common transdermal patch contains nicotine and is used to quit the habit of tobacco smoking. Transdermal patches are also in use in the area of hormonal contraceptives (see contraceptive patch).

Components

The main components to a transdermal patch are:

• Liner - Protects the patch during storage. The liner is removed prior to use.
• Drug - Drug solution in direct contact with release liner
• Adhesive - Serves to adhere the components of the patch together along with adhering the patch to the skin
• Membrane - Controls the release of the drug from the reservoir and multi-layer patches
• Backing - Protects the patch from the outer environment

Types of Transdermal Patches

There are four main types of transdermal patches listed below.

Single-layer Drug-in-Adhesive

The adhesive layer of this system also contains the drug. In this type of patch the adhesive layer not only serves to adhere the various layers together, along with the entire system to the skin, but is also responsible for the releasing of the drug. The adhesive layer is surrounded by a temporary liner and a backing.

Multi-layer Drug-in-Adhesive

The multi-layer drug-in adhesive patch is similar to the single-layer system in that both adhesive layers are also responsible for the releasing of the drug. The multi-layer system is different however that it adds another layer of drug-in-adhesive, usually separated by a membrane (but not in all cases). This patch also has a temporary liner-layer and a permanent backing.

Reservoir

Unlike the Single-layer and Multi-layer Drug-in-adhesive systems the reservoir transdermal system has a separate drug layer. The drug layer is a liquid compartment containing a drug solution or suspension separated by the adhesive layer. This patch is also backed by the backing layer.

Matrix

The Matrix system has a drug layer of a semisolid matrix containing a drug solution or suspension. The adhesive layer in this patch surrounds the drug layer partially overlaying it.

See also

• Route of administration