topical agents

Chapter Six: Topical Agents

General Principles of Topical Agents

Topical compounds produce their pharmaceutical effects primarily at the surface to which they are applied. The term topical therefore refers to application on body surfaces, including the skin and body cavities that open to the outside.

Topical application does not necessarily mean that the compound remains entirely on the surface. Some compounds penetrate into deeper tissues or are absorbed into the general circulation. For example, penetration of an antiseptic into the tissues beneath an exposed wound can help prevent deep infection.

Topical drugs may also be applied within body cavities that communicate with the exterior, including the: Oral cavity Nasal cavity Otic cavity Vaginal cavity Colonic cavity

These applications are generally intended to produce local or surface activity. However, absorption from these sites can also produce systemic effects. Buccal tablets and suppositories are examples of preparations that use body cavities as routes for systemic administration.

Topical compounds are broadly divided according to their usual action or use into: Protectives

Antimicrobial and astringent compounds Structure of the Skin

The skin is the main surface on which topical agents are applied. Its major layers and structures include : Epidermis: the outer layer of the skin.

Dermis: the layer beneath the epidermis containing structures such as: Hair follicles

Sebaceous glands Sweat glands

Hypodermis: the deeper layer containing adipocytes, or fat cells. Muscle: located beneath the hypodermis.

Pores: openings through which sweat and other secretions may reach the surface. Topical agents may act on the surface, enter pores, interact with the epidermis, or penetrate into deeper tissues depending on their properties and formulation.