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PHARMACEUTICAL SUSPENSIONS AND EMULSIONS

PHARMACEUTICAL SUSPENSIONS AND EMULSIONS. Coarse Dispersions. Oil-in-water emulsions (o/w) Water-in-oil (w/o). (Lyophobic colloids). Suspension: Solid drug in liquid vehicle. Emulsion: Liquid drug in liquid vehicle:. Reasons for Use. Drug is insoluble

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PHARMACEUTICAL SUSPENSIONS AND EMULSIONS

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  1. PHARMACEUTICAL SUSPENSIONS AND EMULSIONS

  2. Coarse Dispersions • Oil-in-water emulsions (o/w) • Water-in-oil (w/o) (Lyophobic colloids) • Suspension:Soliddrug in liquid vehicle • Emulsion:Liquiddrug in liquid vehicle:

  3. Reasons for Use • Drug is insoluble • Drug is more stable in suspension or emulsion • There is a need to control the rate of releaseof the drug • Drug hasbad taste (oral)

  4. Routes of Administration • Oral • Ocular • Otic • Rectal • Parenteral • Topical

  5. I. Formulation of Suspensions

  6. Wetting Wetting agent

  7. Well Formulated Suspension • Resuspend easily upon shaking • Settle rapidly after shaking • Homogeneous mix of drug • Physically and chemically stable during its shelf life • Sterile (parenteral, ocular) • Gets into syringe (parenteral, ocular)

  8. “External” Forces Acting on Particles • Sedimentation equilibrium:Gravity is neutralized by Brownian movement Gravity Brownian Movement V(-o)g 2-5 m

  9. Settling and Aggregation • The suspension shall form loose networks of flocks that settle rapidly, do not form cakes and are easy to resuspend. • Settling and aggregation may result in formation ofcakes(suspension) that is difficult to resuspend orphase separation(emulsion) flock cake

  10. Sediment Volume F={volume of sediment Vu}/{original volume Vo} • Vu • Vo • Vo • Vu F=0.5 F=1.0 F=1.5

  11. DLVO: Optimal Distance Energy No flocks can form Repulsion Attraction Attraction Distance

  12. + - Controlled Flocculation • Flocculating agent changes zeta-potential of the particles (it can be electrolyte, charged surfactant or charged polymer adsorbing on a surface). • If the absolutevalue of the zeta-potential is too high the system deflocculates because of increased repulsion and the dispersion cakes. + Non-caking Caking Caking F=Vu/Vo Flocculating Agent - + - + Zeta-potential

  13. II. Formulation of Emulsions

  14. Emulsification Emulsifier

  15. HLB and Use of Surfactants Amphiphilic surfactants are characterized by the hydrophilic-lipophilic balance (HLB): a relative ratio of polar and non-polar groups in the surfactant HLB ca. 1 to 3.5: Antifoams HLB ca. 3.5 to 8: Water-in-Oil Emulsifiers HLB ca. 7 to 9: Wetting and spreading agents HLB ca. 8 to 16: Oil-in-Water Emulsifiers HLB ca. 13 to 16: Detergents HLB ca. 15 to 40: Solubilizers

  16. Required HLB HLB needed for emulsification of the oil phase. If there are several oil ingredients the required HLB is calculated as a sum of their respective required HLB multiplied by the fraction of each. • Calculate the required HLB for the oil phase of the following o/w emulsion: cetyl alcohol 15 g., white wax 1g. Lanolin 2 g, emulsifier (q.s.), glycerin 5 g. water 100 g. • Required HLB Fraction • (from reference) • Cetyl alcohol 15 x 15/18 12.5 • White wax 12 x 1/18 0.7 • Lanolin 10 x 2/18 1.1 • Total required HLB 14.3

  17. HLB of Surfactant Blend Surfactant blends are commonly used to obtain desired emulsifying properties. • What is the HLB of the mixture of 40 % Span 60 (HLB = 4.7) and 60 % Tween 60 (HLB = 14.9)? • HLB of mixture: • 4.7 x 0.4 + 14.9 x 0.6 = 10.8 • In what proportion should Span 80 (HLB = 4.3) and Tween 80 (HLB = 15.0) be mixed to obtain “required” HLB of 12.0? • 4.3.(1-x) + 15.x = 12 x = 0.72 • 72 % Tween 80 and 28 % Span 80

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