Very high logP = highly lipophilic Won’t partition into the water phase very quickly and this can become an issue USP <729> Globule Size Distribution in Lipid Injectable Emulsions o Dynamic light scattering or laser light scattering help determine particle size o Light obscuration method to determine large globules Indicators to assess stability o Macroscopic Look at the emulsion and can tell if it’s separated o Globule size Usually can only tell with a microscope o Viscosity May decrease significantly and form a layer that completely separates Situations: o Flocculation – aggregation of dispersed globules or particles into loose clusters o Coalescence – flocculation --> coalescence Droplets merging to form a single, larger droplet o Cracking – coalescence of dispersed globules and separation of dispersed phase as a separate layer Redispersion is not possible by shaking o Creaming – formulation of a layer of relatively concentrated emulsion CAN BE MADE HOMOGENOUS AGAIN BY SHAKING Less serious type of instability than cracking Large droplets can cream more rapidly, coalesce more readily tin the cream layer Layer can form at the top or bottom depending on specific gravity Factors affecting stability: o Addition of emulsifying agent of opposite type (FYI) o Decomposition/precipitation of emulsifying agents Alkali soaps are decomposed by acids If you add acid to an emulsion, the emulsifier may decompose Sodium/potassium salts can be salted out If you use too much sodium/potassium, you get a common ion effect o Too much sodium and emulsifying agent will precipitate Gums, gelatin, & Casein are INSOLUBLE IN ALCOHOL Large amount of alcohol will render medium hydrophobic & precipitate o Addition of electrolyte Calcium ions can destabilized emulsions by changing from O/W to W/O emulsion Monovalent salts destabilize the emulsion by changing the zeta potential
Disturbs the boundary layer for oil droplets When dispersed particles change charge, the repulsion between the boundary layer and surface charge becomes smaller, so particles come together and tend to coalesce o Can lead to cracking or creaming o Addition of a common solvent When you add a liquid that both dispersed and continuous phase are soluble in, you form a solution instead of an emulsion Drug that originally was soluble in oil may precipitate due to change in solvent o Microbial action Some emulsifying agents are excellent media for growth i.e. gums o Make sure you consider whether you should use a preservative or not o Incorporation of excess disperse phase Emulsion with dispersed phase concentration > 60% have tendency to crack o Droplet aggregation/movement (FYI)
Pharmaceutical Suspension Define suspension, objectives of suspension dosage form, and biopharmaceutics of drug availability from suspensions Suspension – dispersion of finely divided, insoluble solid particles in a fluid o
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- Fall '09
- Colloid, Emulsion, Stratum Corneum, Formulate