Topical Agents Overview

Topical agents are applied to body surfaces and primarily act on the surface of application, though they can penetrate deeper tissues, leading to both beneficial and detrimental systemic effects.
Types of topical agents:
- Protective agents
- Antimicrobial agents
- Astringent agents

Protectives are compounds that shield the skin from irritation, usually of mechanical origin.
Key properties of protectives:
- Insoluble: Limits absorption through the skin, resists washing, and diminishes metallic properties on tissue.
- Chemically inert: Prevents interaction with tissue, ideal protectives are biologically inactive.
- Adsorbents: Absorb moisture from the skin's surface, lessening friction and irritation.
Smaller particle size increases the effectiveness of protectives, as it allows for increased surface area for adhesion and moisture absorption.
Common forms of protectives: powders, ointments, suspensions.

Talc is a hydrous magnesium silicate often with a small amount of aluminum silicate.
Common properties of talc:
- Fine, white to grayish white, crystalline powder
- Unctuous, adheres to the skin, and is free from grittiness.
- Softest mineral known, with a smooth, greasy feel
- Odorless, tasteless, and insoluble in water, dilute acids, and bases.
- Low adsorptive properties
Hydrothermal method can be used to synthesize talc by reacting magnesium oxide or a magnesium salt with silica in an aqueous solution at elevated temperatures and pressures.
Chemical formula of talc: Mg₃Si₄O₁₀(OH)₂
Uses of talc:
- Lubricating, protective dusting powder, preventing friction and irritation.
- Cosmetic preparations (perfumed)
- Medicated preparations with antimicrobial agents, like boric acid.

Zinc Oxide (ZnO) is a fine, odorless, amorphous, white to yellowish white powder, devoid of gritty particles, gradually absorbing carbon dioxide from air.
Properties of Zinc Oxide:
- Insoluble in water and alcohol.
- Reacts with dilute acids and aqueous solutions of ammonium compounds, forming water-soluble products.
- Forms zinc chloride (Lewis acid) when reacted with dilute hydrochloric acid.
Uses of Zinc Oxide:
- Mild astringent and weak antimicrobial
- Astringent and protective in ointments, treating skin ulcerations and other dermatological problems.
- Primary ingredient in Calamine

Calamine is zinc oxide with a small proportion of ferric oxide, giving it a pink color.
Properties of Calamine:
- Fine powder, odorless, practically tasteless
- Insoluble in water but soluble in mineral acids.
Uses of Calamine:
- Topical protective
- Dusting powders, ointments, and lotions, providing soothing, absorbent, and protective properties.

Antimicrobial agents are compounds and preparations used to prevent or reduce infections caused by microorganisms.
Terms associated with antimicrobial agents:
- Antiseptic: Kills or inhibits microorganisms growth when applied to living tissues.
- Germicide: Kills microorganisms outright, including:
  - Bactericides: Kills bacteria.
  - Fungicides: Kills fungi.
  - Amebicides: Kills protozoa.
- -stat: Refers to agents that inhibit microbial growth without killing them (e.g., bacteriostat inhibits bacteria multiplication).
- Disinfectant: Kills microorganisms on inanimate objects but is not safe for living tissue.
- Sterilization: Completely removes or kills all microorganisms from an object, rendering it sterile.
Mechanisms of action of inorganic antimicrobial agents:
- Oxidation: Compounds that are generally nonmetals and certain types of anions. The most common examples include:
  - Hydrogen peroxide
  - Metal peroxides
  - Permanganates
  - Halogens (chlorine and iodine)
  - Oxo-halogen anions
- Halogenation:
- Protein Precipitation:

Sodium hypochlorite solutions are strong oxidizing agents. When reacted with water, it forms hypochlorous acid: NaOCl + H2O ⟶ HOCl + NaOH.
Uses of Sodium Hypochlorite Solutions:
- Disinfectant
- Laundry bleach
- Antiseptic on pus-forming wounds (historically, but not preferred due to its potential to dissolve sutures and blood clots)
- Foot bath for prevention of fungal infections (e.g., athlete's foot)
Diluted Sodium Hypochlorite Solution (N.F.XIII):
- Reduced caustic action on tissues by reducing pH with sodium bicarbonate solution.
- Increases the effective concentration of hypochlorous acid.
- Antibacterial effectiveness is potentially increased by acidifying the solution.

Iodine Solution and Iodine Tincture contain the same concentrations of ingredients, but differ in their solvents: Iodine Solution is aqueous (water), and Iodine Tincture contains alcohol.
Both solutions are transparent and reddish-brown, with the characteristic odor of iodine.
Iodine Tincture also has the odor of alcohol.
Antimicrobial Agent: Iodine
Chemical property in solution: Mild oxidizing agent through the formation of hypoiodous acid [HIO].
Uses of Iodine Solution and Tincture:
- Used as antiseptics
- Used to treat minor wounds or infections due to their broad-spectrum antimicrobial activity

Chemical property: Silver ion (Ag⁺) is a strong protein precipitant, acting on both bacterial and human proteins.
Uses of Silver Nitrate:
- Antibacterial in solutions ranging from 0.01 to 10%, with higher concentrations showing astringent and irritant properties.
- Silver Nitrate Ophthalmic Solution (1%): Instilled into the eyes of newborns as a prophylactic measure against gonococcal infections (ophthalmia neonatorum).
- 0.5% aqueous solution as a wet dressing on third-degree burns.
Side effect: Prolonged use can cause argyria, a darkening of the skin due to silver deposition under the epidermis, and is generally irreversible.

Astringents cause protein precipitation on the surface of cells, coagulating proteins and constricting tissue without causing deep damage.
Mechanism: Act on smooth muscle in small blood vessels.
Uses of Astringents:
- Styptic action: Stop bleeding from small cuts by promoting blood coagulation and constricting capillaries.
- Antiperspirant: Decrease sweat secretion.
- Constrict mucous membranes: Reduce inflammation by limiting blood flow to the surface.