Physical Pharmacy - Surface Active Agents (Lecture 4)

Flashcards covering the definition, classification, mechanisms, and pharmaceutical applications of surface active agents (surfactants) based on lecture notes.

Surface active agents (Surfactants; SAA)

Amphiphilic compounds in which there is a clear separation between lyophilic/hydrophilic (solvent-liking) and lyophobic/hydrophobic (solvent-hating) regions of the molecule.

Lyophilic / hydrophilic

Solvent-liking.

Lyophobic / hydrophobic

Solvent-hating.

Mechanism of SAA activity

Adsorption at an interface where adhesive forces with water increase and the contracting power of the surface decreases, leading to a decrease in tension.

Anionic SAA

Ionic surfactants with a polar head consisting of carbonate, sulfate, sulfonate, or phosphate and a non-polar tail of 12 – 18 carbon atoms.

Sodium lauryl sulfate

A water-soluble anionic surfactant used as a preoperative skin cleaner, a bacteriostatic against gram +ve bacteria, and in medicated shampoo.

Cationic SAA

Surfactants with a cationic charge on the nitrogen atom (e.g., quaternary ammonium) that are bactericidal against gram +ve and gram -ve bacteria; for external use only due to internal toxicity.

Cetirimide

A cationic surfactant used for cleaning wounds and burns or as an emulsifying agent in o/w creams.

Benzalkonium chloride

A cationic surfactant used for cleaning wounds, as a preservative in eye drops, and for preoperative skin disinfection.

Zwitterionic SAA

Surfactants with both anionic (carboxylate, phosphate) and cationic (amine, quaternary ammonium) groups in the polar head; example: Phospholipids (Lecithins).

Non-ionic surfactants

The major class of SAA used in pharmaceuticals because they are safe, stable, and compatible; categorized into Macrogol ethers, Sorbitan esters, Polysorbates, and Block copolymers.

Macrogol ethers

Poly(oxyethylene) glycol ethers of linear fatty alcohols; examples include Cetomacrogol, Brij series, and Cremophor EL.

Sorbitan esters (Spans®)

Water-insoluble lipophilic surfactants used as w/o emulsifiers and wetting agents; examples include Span 20, 40, 60, 65, 80, and 85.

Ethoxyated sorbitan esters (Polysorbates or Tweens®)

Water-soluble hydrophilic surfactants used as o/w emulsifiers, solubilizing agents for oily vitamins, and wetting agents; examples include Tween 20, 60, and 80.

Block copolymers

Macromolecules consisting of monomer blocks that differ in composition, such as Poloxamers (Pluronics®); used as o/w emulsifiers, solubilizing agents, and wetting agents.

HLB (Hydrophilic-Lipophilic Balance)

An arbitrary scale of values (1 - 20) created by Griffin to measure the balance of SAA; higher values indicate greater hydrophilicity.

Antifoaming agents

Surfactants with an HLB value of $2-3$.

w/o Emulsifying agents

Surfactants with an HLB value of $3-6$.

Wetting and spreading agents

Surfactants with an HLB value of $7-9$.

o/w Emulsifying agents

Surfactants with an HLB value of $8-16$.

Detergents

Surfactants with an HLB value of $13-15$.

Solubilizing agents

Surfactants with an HLB value of $15-18$.

Critical micelle concentration (CMC)

The concentration of SAA above which micelles form and all additional SAA added to the system form further micelles.

Micelles

Spherical aggregates in an aqueous phase where non-polar tails form a hydrophobic core and polar heads form a hydrophilic shell.

Reverse micelles

Aggregates in a non-aqueous phase with a polar core and a non-polar shell.

Wetting agent

A surfactant that lowers the contact angle and displaces the air phase at a surface, replacing it with a liquid phase.

Iodophors

Solubilized solutions of iodine in non-ionic surfactant micelles used for instrument sterilization.

Foaming agent

Surfactants used in shampoo that lower the surface tension of water and create micelles around dirt and oil to be removed during rinsing.