DS - Creams And Suspensions.

Question 1

Define suspensions and list their main applications

Answer 1

Pharmaceutical suspensions are made of solid particles with low solubility dispersed in an other phase e.g. an aqueous liquid.
Pharmaceutical suspensions are colloidal suspensions

Characteristics
Particles (dispersed phase) size: from 0.5 mm to 100mm. Coarse particles BUT treated as colloidal systems
High concentration of drugs are used (more than 2%w/v) Examples of use:
Unpalatable soluble drugs given as insoluble form to hide unpleasant taste
Lotions used to deposit fine powder on skin surface Slow release formulation to give a prolonged effect
Pharmaceutical Suspensions
Definition

Question 2

Explain why flocculation is necessary in pharmaceutical suspensions

Answer 2

Flocculation
• Important aspect for pharmaceutical suspensions
Definition of a floc or flocculate
• A flocculate or floc is a cluster of particles held together in a loose open structure (i.e. two particles are attached via VdW forces for a while then separate)
• Flocs are spontaneously formed and broken down

Influence of DLVO theory
• It means that moderately deep secondary minimum are required for their formation (decrease of repulsion potential).
Characteristics of a flocculated suspension
• Sediment contains voids
• High volume,
• Rapidly obtained,
• Easy to re-disperse,
• No problems from caking
• Depends on electrolytes and type

Question 3

Explain how flocculation is controlled inpharmacenticall suspensions

Answer 3

Schultz-Hardy rule
• Ions arranged in order of their capacity to aggregate hydrophobic colloids i.e. flocculation depends on the charge number of ion and is independent of the type of ion.
• Although trivalent are more efficient they are less used than monovalent ions (toxicity)
Most common ions
• sodium salts of acetates, phosphates and citrates
Example: to flocculate AgI solutions, one require:
• 140 mmol/L of NaNO3
• 2.40 mmol/L of Ca(NO3)2 • 0.067 mmol/L of Al(NO3)3

Addition of polymers
Examples of polymers used
Starch alginates, cellulose derivatives, tragacanth, carbomers and silicate
How does it work?
Linear branched-chains form gel-like network within system and become adsorbed on the dispersed particles: protective colloids
During manufacture, blending must not be
excessive as may inhibit crosslinking between adjacent particles: results in a deflocculated system
High concentration may have similar effect
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