Pharmaceutical suspensions and emulsions
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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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Coarse dispersions l.jpg
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:


Reasons for use l.jpg
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)


Routes of administration l.jpg
Routes of Administration

  • Oral

  • Ocular

  • Otic

  • Rectal

  • Parenteral

  • Topical



Wetting l.jpg
Wetting

Wetting agent


Well formulated suspension l.jpg
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)


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“External” Forces Acting on Particles

  • Sedimentation equilibrium:Gravity is neutralized by Brownian movement

Gravity

Brownian Movement

V(-o)g

2-5 m


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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


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Sediment Volume

F={volume of sediment Vu}/{original volume Vo}

  • Vu

  • Vo

  • Vo

  • Vu

F=0.5

F=1.0

F=1.5


Dlvo optimal distance l.jpg
DLVO: Optimal Distance

Energy

No flocks can form

Repulsion

Attraction

Attraction

Distance


Controlled flocculation l.jpg

+

-

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



Emulsification l.jpg
Emulsification

Emulsifier


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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


Required hlb l.jpg
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


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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