colloid an introduction kausar ahmad kulliyyah of pharmacy physical pharmacy 21
TRANSCRIPT
Colloid An Introduction
Kausar Ahmad
Kulliyyah of Pharmacy
http://staff.iium.edu.my/akausar
Physical Pharmacy 2 1
Physical Pharmacy 2
Contents
Lecture 1:• Types of colloids• Types of dispersions
Lecture 2:• Types of emulsions• Emulsification factors
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Colloidal System
Particle size below 1 mm
High specific surface area
Discrete particles dispersed in a different medium
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Types of Colloids
TypeDispersed
phaseContinuous
phase
Emulsion: o/w oil water
Emulsion: w/o water oil
Suspension solid water or oil
Aerosol solid or liquid air
Others Multiple emulsion: w/o/w, o/w/o
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Classification Based on Size
Class Size Examples
Molecular dispersion
< 1.0 nm glucose
Colloidal dispersion
1.0 nm - 0.5 mm Natural rubber latex
Coarse dispersion
> 0.5 mm red blood cells
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Classification of dispersed systems
hydrophilic colloidal dispersion (in water)• surfactant micelles and phospholipid vesicles, also
known as association colloids
lyophilic colloids• proteins, gelatin • rubber, gum
lyophobic/hydrophobic colloids • gold, silver and sulfur• emulsion
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Physical Pharmacy 2
Colloidal Phenomena
detergencymilk
coconut milk
ice-cream
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Pharmaceutical suspensions
Coarse dispersions
• Solid-in-liquid
Main function
• Delivery vehicle for suspended drug particles
Surfactant/dispersant reduces interfacial energy
• Stabilisation by electric repulsive force & steric hindrance effect
Examples: Oral suspensions, topical applications, injectables
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Preparing a Dispersion
Particle size reduction
surface of each primary particle is available to liquid.
Wetting of powder
wet external surfaces & displace air
between internal clusters.
Dispersing by using charged
bulky surfactants
Provide strong interfacial layer
Modifying the viscosity
to minimise sedimentation
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Properties of dispersing agents
adsorption of surfactants at the solid/liquid
interface.
highly charged
provide steric hindrance
END OF LECTURE 1 OF 2
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Pharmaceutical Emulsions
Emulsion• liquid-in-liquid vehicle• o/w or w/o
Main function• provide vehicles for drug delivery and parenteral nutrition. • drug is dissolved in the water or oil phase.
Surfactant/emulsifier reduces interfacial energy• emulsion becomes thermodynamically stable
Examples:• parenterals, creams, lotions
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Emulsification
Physical Pharmacy 2
WATER
OIL
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homogeniser
emulsifier
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Emulsification Factors
Concentration of dispersed/oil phase
Types & concentrations of
surfactants
Emulsifying temperature
especially for non-ionic surfactants
Type of homogeniser
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Types of Emulsions
Macroemulsion Nanoemulsion
Microemulsion Multiple emulsion
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Physical Pharmacy 2
Nanoemulsion and Microemulsion
Nanoemulsions: 50-200 nm
Microemulsions: 5-50 nm
LONG TERM PHYSICAL STABILITY AGAINST…….
CREAMING, FLOCCULATION AND COALESCENCE
Due to small size they enhance penetration, spreading and will give uniform distribution on the substrate on which they are applied.
Examples: personal care products and cosmetics, agrochemicals, pharmaceuticals, household products etc.
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Methods of Preparation
Nanoemulsions are easily formulated using high-pressure homogenizers with proper choice of surfactants and/or polymers.
The production of microemulsions may employ the Phase Inversion Temperature (PIT) principle.
These emulsions are stabilised through steric stabilization and by the thickness of the adsorbed layer.
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Multiple Emulsion
Dispersed phase contains droplets of another phase.
o/w/o or w/o/w.
Prepared through a double homogenization process or a one step procedure using the PIT.
Both are important for drug delivery.
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Example of w/o/w emulsion for drug delivery by intra-muscular route
Advantage of w/o:
slow-release because drug has to diffuse through oil
Disadvantage:
viscosity of medium (oil) is high
Solution:
to disperse the w/o in aqueous medium.
• On injection, the aqueous phase dissipates rapidly leaving behind the w/o.
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Physical Pharmacy 2
Multiple Emulsion for PharmaceuticalsExamples
Sandostatin LARTM Depot
Novartis (hypothalamic hormones analogue)
Control of hypersecretion at the site of the tumour where
hormone overproduction starts
Human NutropinTM Depot
Alkermes/Genentech (human insulin suspension)
somatropin (rDNA origin) for injectable suspension
long-acting dosage form of recombinant human growth
hormone (rhGH).
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Multiple emulsion Pharmaceutical Problems
• typically accounts for 10-80% of the total drug loading. • This ‘initial burst’ poses a toxicity threat & is a major
hurdle for the development of microspheres.
Rapid release during the first day
• This can last for weeks and is referred to as the ’lag-time’. • During this induction period, the patient is not effectively
treated due to lack of drug release.
Very slow release period after the initial burst period.
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Physical Pharmacy 2
References
PC Hiemenz & Raj Rajagopalan, Principles of Colloid and Surface
Chemistry, Marcel Dekker, New York (1997)
HA Lieberman, MM Rieger & GS Banker, Pharmaceutical Dosage
Forms: Disperse Systems Volume 1, Marcel Dekker, New York (1996)
F Nielloud & G Marti-Mestres, Pharmaceutical Emulsions and
Suspensions, Marcel Dekker, New York (2000)
J Kreuter (ed.), Colloidal Drug Delivery Systems, Marcel Dekker,
New York (1994)
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