Topical Agents Overview

Topical Agents

• Topical compounds are applied to the surface of the body.
• They have a localized effect, but can be absorbed and cause systemic effects.
• They are categorized into protective agents, antimicrobial agents, and astringent agents.

Protective Agents

• Protectives are insoluble and chemically inert.
• They protect the skin from mechanical irritation.
• They act as adsorbents, absorbing moisture and reducing friction.
• They are typically used as powders, ointments, or suspensions.

Talc

• Talc is a hydrous magnesium silicate.
• It is a very fine, white or grayish white, crystalline powder.
• It is unctuous, adheres readily to the skin, and is free from grittiness.
• It is odorless, tasteless, and insoluble in water, dilute acids, and dilute bases.
• It has very low adsorptive properties.

Calamine

• Calamine is a topical protective.
• It is obtained by calcining zinc carbonate.
• It is used in dusting powders, ointments, and lotions for its soothing, adsorbent, and protective properties.

Antimicrobial Agents

• Antimicrobial agents prevent and reduce infections caused by microorganisms.
• Antiseptics kill or inhibit the growth of microorganisms on living tissues.
• Germicides kill microorganisms outright.
• -stat agents (e.g., bacteriostat) inhibit the growth of microorganisms.
• Disinfectants kill microorganisms on inanimate objects.
• Sterilization completely removes or kills all microorganisms.

Mechanisms of Action of Inorganic Antimicrobial Agents

• Oxidation: Compounds like hydrogen peroxide, permanganates, and halogens oxidize proteins.
• Halogenation: Hypohalite and hypochlorite antiseptics react with protein molecules, altering their conformation.
• Protein Precipitation: Metallic ions with high charge/radius ratios or strong electrostatic fields precipitate proteins, affecting their function.

Hydrogen Peroxide (H₂O₂)

• Hydrogen Peroxide solution is a clear, colorless liquid.
• It is unstable and deteriorates upon standing or agitation.
• It decomposes when in contact with oxidizing or reducing substances.
• It is used as an antiseptic.

Iodine

• Iodine is a very active element.
• It is easily inactivated by organic materials in the gastrointestinal tract.
• Ingestion of large quantities can cause corrosive action on the gastrointestinal tract.
• Iodine solutions are used as topical antiseptics (Iodine Tincture and Iodine Solution) and to disinfect drinking water.

Povidone-iodine

• Povidone-iodine is an iodophor, a complex of iodine with a carrier organic molecule.
• It slowly releases iodine in solution.
• It is used as a topical antiseptic because it is less irritating than iodine tinctures.

Silver Nitrate (AgNO₃)

• Silver Nitrate is a colorless or white crystal that becomes gray or grayish black when exposed to light.
• It is very soluble in water.
• Solutions of silver nitrate (0.5-1.0%) are used as antibacterial agents.
• Silver ions precipitate both bacterial and human proteins, leading to antibacterial, astringent, irritant, and corrosive effects.
• Prolonged use can cause argyria, a darkening of the skin due to silver deposition.
• It is used as an antibacterial, prophylactic measure against ophthalmia neonatorum, and in burn treatment.

Astringents

• Astringents precipitate proteins on the surface of cells, causing coagulation and tissue constriction.
• They have limited penetration and do not cause the death of cells.
• They are used as styptics (stop bleeding), antiperspirants, and to constrict mucous membranes.