Transdermal Drug Delivery Systems

Transdermal drug delivery systems or TDDS use patches to release drugs through the skin into systemic circulation at a controlled rate.

These systems benefit drugs with short half-lives or narrow therapeutic indices by maintaining stable plasma levels.

They include monolithic systems—in which drugs are embedded in a polymer matrix—and reservoir systems—in which drugs are stored in a compartment with a rate-controlling membrane.

Mixed systems combine both types, offering an initial controlled release followed by diffusion through the matrix.

Two steps limit the choice of TDDS: diffusion from the patch and skin permeation.

Advantages include noninvasive application, bypassing GI degradation and first-pass metabolism, and good patient compliance.

However, they are unsuitable for high-dose drugs, large molecules, extremely lipophilic or hydrophilic compounds, skin irritants, or drugs heavily metabolized in the skin.

Common examples of transdermal delivery systems include scopolamine and contraceptives like Ortho Evra.