Suspension

1. Suspension KhSadique Faisal Asst. Lecturer Northern University Bangladesh

2. Formulation of suspension During the preparation of physically stable pharmaceutical suspensions, a number of formulation components are used to keep the solid particles in a state of suspension (suspending agents), whereas other components are part of the liquid vehicle itself and have other functions in the dosage form.

3. Formulation of suspension • 1. Components of the suspending system • Wetting agents • Dispersants or deflocculating agents • Flocculating agents • Thickeners • 2. Components of the suspending vehicle or external • phase • pH control agents and buffers • Osmotic agents • Coloring agents, flavors, and fragrances • Preservatives to control microbial growth

4. Wetting Agent • Wetting agents are surfactants that lower the interfacial • tension and contact angle between solid particles • and the liquid vehicle. When the insoluble powder is • added to a liquid vehicle containing a wetting agent, • penetration of the liquid phase into the powder will • be sufficiently rapid to permit air to escape from the • particles. The resulting wetted particles either sink en

5. Wetting Agent masse or separate with low-shear agitation. The best range for wetting and spreading by non-ionic surfactants is between a hydrophile–lipophile balance (HLB) value of 7 and 10, although surfactants with values higher than 10 are often used for this purpose. Common wetting agents and surfactants include: 1) anionic type (docusate sodium and sodium lauryl sulfate) and 2) non-ionic type (polyoxyalkyl ethers, polyoxylakyl phenyl ethers, polyoxy hydrogenated castor oil, polyoxysorbitan esters, and sorbitan esters).

6. Deflocculants and Dispersing Agents Unlike surfactants, these agents do not appreciably lower surface and interfacial tension; thus, they have little tendency to create foam or wet particles. Most deflocculants, however, are not generally considered safe for internal use, and as a result the only acceptable dispersant for internal products is lecithin or a lecithin derivative (naturally occurring mixture of phosphatides and phospholipids). Because lecithins vary in water solubility and dispersibility characteristics, proper control of product specifications must be maintained to obtain reproducibility.

7. Flocculating Agents Primary flocculating agents are simple neutral electrolytes in solution that are capable of reducing the zpotential of suspended charged particles to zero. Small concentrations (0.01–1%) of neutral electrolytes, such as sodium or potassium chloride, are often sufficient to induce flocculation of weakly charged, water-insoluble, organic non-electrolytes. In the case of highly charged, insoluble polymers and polyelectrolyte species, similar concentrations (0.01–1%) of water-soluble divalent or trivalent ions, such as calcium salts, alums, sulfates, citrates, and phosphates, may be required for floc formation, depending on particle charge (positive or negative). These salts are often used together as pH buffers and flocculating agents.

8. Thickeners, Protective Colloids, andSuspending Agents Protective or hydrophilic colloids, such as gelatin, natural gums, and cellulosic derivatives, that are adsorbed on insoluble particles, increase the strength of the hydration layer formed around suspended particles through hydrogen bonding and molecular interaction. Because these agents do not reduce surface and interfacial tension, they function best in the presence of a wetting agent. Many of these agents are protective colloids in low concentration (<0.1%) and viscosity builders in higher concentrations (>0.1%). Suspending agents commonly used in pharmaceutical suspensions include: