Definition
A flocculated suspension is one in which solid particles form loose, fluffy aggregates called flocs.
These flocs settle quickly but can be easily redispersed upon shaking.
Flocculated suspensions are preferred in pharmaceuticals due to their better stability and ease of redispersion.
Preparation of Flocculated Suspensions
a. Particle size reduction:
The solid drug is milled or micronized to achieve a suitable particle size for proper dispersion in the liquid medium.
b. Wetting of particles:
A wetting agent is used to reduce interfacial tension between solid particles and the liquid medium.
c. Formation of flocs:
A flocculating agent, such as electrolytes or polymers, is added to the mixture to promote the formation of loose, easily dispersible flocs.
d. Controlled flocculation:
The flocculating agent concentration is adjusted to achieve the desired degree of flocculation without causing excessive settling or caking of the particles.
Stability problems & Method to overcome
a. Sedimentation:
Problem: Rapid settling can lead to uneven dosing and difficulty in redispersion.
Solution: Adjust flocculating agent concentration and increase the viscosity of the medium with thickening agents like hydroxyethyl cellulose or xanthan gum to slow sedimentation.
b. Caking:
Problem: If flocs settle too tightly, they may form a hard cake that is difficult to redisperse.
Solution: Optimize flocculation by adjusting flocculating agents and increasing viscosity with suitable thickeners. Shake the suspension gently before use.