Suspensions in Pharmaceutics

Suspensions

• Suspensions are liquid dosage forms where insoluble or poorly soluble drugs are dispersed in a liquid.
• They offer advantages like:
  • High bioavailability due to large surface area of dispersed drug, ensuring rapid dissolution and absorption.
  • Chemical stability for drugs that are unstable in solution but stable in suspension.
  • Improved palatability compared to solutions, especially for poorly tasting drugs.
• Desired features of suspensions:
  • Therapeutic efficacy.
  • Chemical stability of components.
  • Permanency of the preparation.
  • Aesthetic appeal.
• Specifications of suspensions:
  • Slow settling rate with easy redispersion when shaken.
  • Stable particle size over time.
  • Pour-ability and flow through syringes.
• Ideal suspensions exhibit physical stability, meaning particles remain uniformly distributed.
• Settling rate of particles is governed by Stoke's Law, which considers factors like:
  • Particle diameter (d)
  • Particle density (ρi)
  • Medium density (ρe)
  • Gravitational constant (g)
  • Medium viscosity (η)
• Factors affecting sedimentation rate:
  • Smaller particle size leads to slower settling rate.
  • Higher particle density results in faster settling.
  • Increased viscosity of the medium slows down sedimentation.
• Particle size reduction techniques:
  • Micropulverization: Produces particles 10-50 μm, suitable for most oral and topical suspensions.
  • Fluid energy grinding (jet milling): Produces particles under 10 μm, suitable for parenteral and ophthalmic suspensions.
  • Spray drying: Creates extremely small particles, used for specialized applications.
• Advantages of particle size reduction includes:
  • Reduced sedimentation rate for better stability.
  • Slow, uniform settling.
• However, excessive particle size reduction can create a compact cake, which is difficult to redisperse.
• Shape of particles also influences caking:
  • Symmetrical particles like barrel-shaped calcium carbonate form stable suspensions.
  • Asymmetrical particles like needle-shaped calcium carbonate tend to form tenacious sediment cakes.
• Flocculation prevents caking:
  • Flocculating agents like bentonite magma create loose aggregates (flocs) that resist compaction.
  • Flocs settle faster but are easily redispersed.
• Comparison of deflocculated and flocculated suspensions:
  • Deflocculated: Particles settle slowly, forming a compact cake.
  • Flocculated: Particles settle rapidly, forming a loose sediment that is easily redispersed.
• Methods of flocculation:
  • Clays like bentonite magma act as flocculating agents in oral suspensions.
  • pH adjustment can induce flocculation in parenteral suspensions.
  • Electrolytes can bridge particles and promote flocculation.
  • Carefully chosen surfactants can also induce flocculation.
• Suspending agents are used to thicken the dispersion medium and prevent settling.
• Examples of suspending agents include:
  • Carboxymethylcellulose (CMC)
  • Methylcellulose
  • Microcrystalline cellulose
  • Xanthan gum
  • Polyvinylpyrrolidone
  • Bentonite
• Important considerations for suspending agents are:
  • Avoiding interference with drug availability.
  • Avoiding viscosity that hinders agitation and pouring.
• Key difference between suspensions and colloids:
  • Size of dispersed particles: Suspensions have larger particles prone to sedimentation.
• Suspensions share many other properties of colloidal systems.

Explore the characteristics and advantages of suspensions as liquid dosage forms in this quiz. Understand their importance in providing high bioavailability and chemical stability for drugs. Test your knowledge of the desired features and specifications that make suspensions effective and appealing.