Pharmaceutics Exam 3 (Lecture 33- Compounding Suspensions)

Dispersion

Two phase system where one phase is distributed as particles into another phase

Dispersed Phase

• Also known as internal phase

• comprises of particular solid matter (Insoluble in external phase)

Continuous Phase

• Also known as external phase or dispersion medium

• Generally liquid or semisolid (Gel, cream, ointments)

Emulsion

Liquid in Liquid

Suspension

• Solid in liquid (or semisolid)

• Can be sterile/nonsterile

• appropriate when drug is not sufficiently soluble or chemically stable in a solvent

• Must be uniformly dispersed throughout the vehicle

Advantages of a suspension

• Easy to swallow (children/elderly)

• Flexibility when measuring

• More stable when dispersed

• Taste can be masked

• Can be extended/delayed/controlled release

• Aesthetic

Factors to consider when making suspensions

• Wettability of suspended solid

• Size of suspended particles

• Viscosity

Wetting Agents

• Many are surfactants

• Decrease interfacial tension between solid and aqueous medium

• Increase dispersibility

Wettability of suspended solid

Ability of liquid to adhere to or spread across a solid surface

• Determined by balance between adhesive and cohesive forces

Size of suspended particles

• size reduction leads to compact cake sedimentation

• To make particles smaller: Mill or grind

• Size can affect absorption, dissolution, and biodistribution

Viscosity

Greater Viscosity= slower sedimentation

Shear-thinning is good

Flocculation

create a network of weakly held particles that sediment quickly

• due to large particle size, they do so in large, loose clumps that resemble a cloud in liquid.

• easy to redispurse by shaking

• You can induce this by electrostatic potential or steric hinderance

Deflocculated Suspensions

• Individual particles are dispersed throughout external phase

• Small particle size

• high viscosity

• do not stick to walls

• sedimentation is very slow

• hard to resuspend

• cloudy supernatant

Flocculated suspensions

• particles form loose aggregates

• sedimentation rate is high

• low viscosity

• adhere to container walls

• easily resuspend

• not aesthetically pleasing

Tituration

Decreasing particle size of powder by grinding them down w/ mortar/pestle

Levigation

same as titration but small amount of liquid added (insoluble) to form a paste

Levigation Agent

Viscous, low surface tension to wet solid particle, act as lubricants allowing easier incorporation

Geometric Dilution

Mixing Small amount of powder API with large amount of excipient (added via dilution method)