What is a significant disadvantage of topical administration?

Topical administration involves delivering medication directly onto the skin or mucous membranes, which can lead to significant local effects. However, one of its notable disadvantages is the potential for systemic toxicity. This occurs because, despite the intention for localized treatment, some drugs can be absorbed through the skin into the systemic circulation, particularly if they are formulated to penetrate well or if the body site has high permeability. Factors like the nature of the formulation, the integrity of the skin barrier, and area of application can influence the extent of systemic absorption.

For example, certain topical corticosteroids, when used over large areas or under occlusive dressings, can lead to elevated systemic levels that can result in side effects similar to those seen with oral or injectable forms. This potential for unwanted systemic effects necessitates careful consideration of dosing and application site when using topical medications.