Flocculated suspension

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

1. Particle size reduction:

   • The solid drug is milled or micronized to achieve a suitable particle size for proper dispersion.

2. Wetting of particles:

   • A wetting agent is used to reduce interfacial tension between solid particles and the liquid medium.

3. Formation of flocs:

   • A flocculating agent (e.g., electrolytes or polymers) is added to promote the formation of loose, easily dispersible flocs.

4. Controlled flocculation:

   • The concentration of the flocculating agent is adjusted to achieve the desired degree of flocculation without excessive settling or caking.

Stability Problems & Solutions

1. 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.

2. 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.

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