Compared to emulsion: both disperse phase but emulsion is liquid in liquid while suspension is solid in liquid Advantages: o Administer water insoluble drugs BIGGEST ADVANTAGE o Prolong DOA Depot injections o Never use ordinary suspensions via IV or intrathecal route Causes embolism o Bigger AUC than solution for poorly water-soluble drugs o Pediatric and geriatric use Can flavor external phase o Taste masking (good for bitterness) o Topical preparation, to leave a light deposit Disadvantages: o Dosing If you don’t shake well, you may get different doses at different points of time o Long-term stability Poorly soluble drug in contact with water can hydrolyze Understand formulation considerations of pharmaceutical suspensions Physical properties of a good suspension: o Remains suspended long enough to administer o Settling particles don’t form a hard cake o Product should be viscous enough to give uniform dose o Be composed of small and uniform particles (not gritty) 4 steps: o Particle size reduction Small particles stay afloat for a longer time V is proportional to r in Stoke’s Law o Wetting Remove hydrophobic layer of air from the particle surface Particles will remain on the surface of the liquid in the absence of proper wetting Without wetting, each particle has a thin layer of air around it o Controlled flocculation Reduces the surface charge that causes repulsion and deflocculation Suspension stability is dependent on Zeta potential
If zeta potential is reduced (below a critical value), the degree of repulsion is lower, and particles come closer together to flocculate o Zeta potential is reduced by adding electrolyte Can’t add too much because then the particle will adsorb the charge and you’ll have the same issue, but with the opposite charge o Structured vehicles To increase stability, must decrease viscosity Use structured vehicle in pharmacy made of hydrocolloids that are mostly negatively charged o Most hydrocolloids are negatively charged o Problem with hydrocolloid: Precipitate with alcohol Overall, have decreases stability Understand importance of flocculation and deflocculation in suspension stability Flocculated particles o Loose aggregates o Rate of settling is high Due to Stoke’s law Velocity is proportional to the radius of the particles & the flocks have greater radius to cause quicker settling Increased effect particle size o Apparently unpleasant o Fast sediment formation o Loosely packed sediment o EASY TO REDISPERSE o DESIRED FOR SUSPENSION Deflocculated particles o Separate particles Prevented from forming flocks by some inherent property Could be charge o Rate of settling is low Decreased effect particle size o Apparently pleasing appearance o Slow sediment formation o Tightly packed sediment o DIFFFICULT TO REDISPERSE o DESIRED FOR EMULSION Both Stoke’s Law & Brownian movement still apply here o
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- Fall '09
- Colloid, Emulsion, Stratum Corneum, Formulate