There are primarily four types of Transdermal patches:
Single-layer Drug-in-Adhesive: The patch contains a layer that is responsible for releasing the drug into the skin which then flows through the bloodstream. It also contains a skin-contacting adhesive layer.
Multi-layer Drug-in-Adhesive: The Multi-layer Drug-in-Adhesive patch is similar to the Single-layer Drug-in-Adhesive patch as the adhesive layer is responsible for releasing the drug. It has multiple layers which serve different purposes. One layer releases a drug immediately and the other layer controls the drug release from the reservoir. There may be a last layer which separates the membrane.
Reservoir: The Reservoir Transdermal patch differs from the earlier patches because it has a liquid compartment that contains drugs. It has a drug layer that separates itself from the adhesive layer. With the reservoir patch, the delivery of the drug is released at a constant rate. The reservoir patch contains the drug and is one of the more common patches used by patients.
Matrix: The Matrix system has a semisolid drug layer that contains a drug solution. This type of patch does not contain any liquid or gel. It is a preferred patch because there are no chances of leakage in the gel.
Components of a Patch
Transdermal patches have several components:
• Liner – Protects the patch during storage. The liner should be removed before use.
• Drug – Drug solution is in direct contact with the release liner.
• Adhesive – Holds the components of the patch together. It also helps keep the patch ‘glued’ to the skin.
• Membrane – Controls the release of the drug from the patch.
• Backing – Protects the overall patch during the application period.