OIA1008 SUSPENSION & EMULSION

Pharmaceutical suspension

A coarse dispersion of insoluble solid particles (typically >0.5 µm) dispersed in a liquid medium.

Examples of suspension dosage forms

Oral (e.g., antacids), parenteral (e.g., vaccines), external (e.g., calamine lotion).

Brownian motion

Zig-zag motion of small particles due to random impact of surrounding molecules; aids dispersion.

Stokes’ Law

v = (2/9)(d₁ – d₂)gr²/η — calculates sedimentation velocity; depends on particle size, density, and viscosity.

Sedimentation

Downward movement of particles under gravity; critical for stability.

Clear liquid zone

Top layer with no suspended particles; increases as sedimentation occurs.

Suspension interface

Boundary between suspended and settled particles; moves down over time.

Constant composition zone

Stable area where particles remain uniformly distributed.

Variable composition zone

Area where particle concentration increases toward the bottom; precursor to aggregation.

Sludge interface

Transition between suspended and settled particles; beginning of compaction.

Sediment

Bottom layer where particles settle; flocculated sediments are loose, deflocculated sediments cake.

Purpose of suspending agents

Prevent sedimentation or caking; maintain even distribution of drug particles.

Ideal properties

Should allow easy redispersion with mild shaking and resist crystal growth or aggregation.

Natural suspending agents

Polysaccharides like acacia, tragacanth, alginates.

Inorganic suspending agents

Bentonite, magnesium aluminum silicate — form gels or structured networks.

Synthetic suspending agents

Methylcellulose, sodium carboxymethylcellulose — widely used due to controlled viscosity.

Controlled flocculation

Ensures particles settle as loose flocs, preventing hard cake formation and allowing easy redispersion.

Deflocculated suspension

Particles settle slowly but compact tightly → caking occurs, making redispersion difficult.

Flocculated suspension

Settles faster but forms loose sediment that's easy to redisperse.

Hydrophilic–lipophilic balance (HLB)

Used to select surfactants that help maintain suspension or emulsion stability.

Pharmaceutical emulsion

Two-phase system of two immiscible liquids (e.g., oil + water), one dispersed as globules in the other.

Thermodynamically unstable

Requires mechanical energy and emulsifying agents to stabilize.

Particle size range

Typically 0.25–25 µm for emulsions.

Emulsifying agents

Surface-active agents that reduce interfacial tension and stabilize droplets.

Oil-in-water (o/w)

Oil droplets dispersed in water; common for oral and topical use.

Water-in-oil (w/o)

Water droplets in oil; used for emollients and slow drug release.

Double emulsions (o/w/o or w/o/w)

Used for prolonged drug release or incompatible drug separation.

Improve solubility & permeability

Increase dissolution of poorly water-soluble drugs.

Enhance bioavailability

Smaller droplet size increases surface area and absorption.

Taste masking

Oil phase masks bitter drugs in oral emulsions.

Topical therapy

Used in dermatology and cosmetics for hydration, drug delivery, and soothing.

IV nutrition and drug delivery

Lipid-based emulsions carry fat-soluble vitamins or poorly water-soluble drugs.

Commonly o/w (oral emulsion)

For better mouthfeel, easier swallowing, and flavoring.

Absorption benefits (oral emulsion)

Drug in oil phase of o/w emulsion may bypass first-pass metabolism via lymphatic uptake.

Dilution with GI fluids

o/w emulsions mix easily with GI fluids → better dispersion and absorption.

o/w type (topical emulsion)

Water-washable, less greasy, suitable for cosmetics and non-oily drug bases.

w/o type (topical emulsion)

Emollient, water-resistant, used for dry skin treatment and slow drug release.

Factors for choice (topical emulsion)

Depends on drug properties, desired absorption, and skin condition.

Intravenous (IV) emulsions

Must be o/w for compatibility; used for nutrition and drug delivery (e.g., diazepam, amphotericin B).

Depot (IM/SC) emulsions

Usually w/o — prolong drug release by delaying diffusion from internal phase to body fluids.