COARSE DISPERSION + PHARMACEUTICAL SUSPENSION

Dispersed System

Consist of particulate matter, known as the dispersed phase, distributed throughout a continuous or dispersion medium.

1. Molecular dispersion

2. Coarse dispersion

3. Colloidal dispersion

Dispersed System consist of what?

• Particle size greater than 0.5 micrometer or 500 nanometers.
• Visible under a microscope.
• Characterized by sedimentation.
• Particles do not pass through normal filter paper
• Examples: suspensions, emulsions, grains of sand, RBC

Characteristics of Coarse Dispersion

SUSPENSION

• A coarse dispersion in which insoluble solid particles are dispersed in a liquid medium

•  Particles have a diameter greater than 0.5 μm 

• Particles exhibit Brownian motion if the dispersion has a low viscosity

Suspended materials should not settle rapidly

• particles that settle should not form a hard cake at the bottom of the container

• must be readily re-dispersed into a uniform mixture when the container is shaken.

• The particles in suspensions should be kept uniformly distributed throughout the dispersion.

Suspension should not be too viscous

to pour freely from the orifice of the bottle or flow throughout of a syringe needle

External lotions

• Should be fluid enough to spread easily yet must be mobile that it runs off the surface to which it is applied 

• It must dry quickly and provide an elastic protective film that will not be rubbed off easily 

• It should have acceptable odor and color

Significance of Pharmaceutical Suspensions

The pharmaceutical suspension is a course dispersion in which insoluble solid particles are dispersed in a liquid medium.

oral administration

Provides a suitable form for ____ of drugs that have limited solubility in the vehicle (usually water) and for better chemical stability of that than the solution.

bitter taste

The ____ of the drug is also better masked if it is in suspension.

dermatologic materials

Provide a suitable form for the application of ____ to the skin and sometimes to the mucous membranes

parenteral administration

Provide a suitable form for___ of insoluble drugs

Oral Suspension

• oral antibiotics - usually contain 125 to 500 mg per 5 mL of solid material 

• antacid and radiopaque suspensions - high 

• concentration of dispersed solid

oral antibiotics

usually contain 125 to 500 mg per 5 mL of solid material

Externally Applied Suspensions

Designed for dermatologic, cosmetic and protective purposes - concentration of the dispersed phase may exceed 20% (20g/100mL suspension)

Parenteral Suspensions

• Contain 0.5 % to 30% solid particles 

• Viscosity and particle size are significant factors because they affect the ease of injection and availability of drugs in depot therapy 

• Administered intramuscularly or subcutaneously

thermodynamically unstable system

the particles are highly energetic and tend to regroup in such a way as to decrease the total area and reduce the surface energy. Thus, particles in liquid suspension tend to flocculate.

Flocculation

formation of light, fluffy conglomerates that are held together by weak Van der Waals forces.

Aggregation

a process where particles adhere by stronger forces (compacted cake). Worse than flocculation

Caking

growth and fusing together of crystals in the precipitate to produce solid aggregates.

Types of Agglomerates

floccules (flocculation) and aggregates (aggregation) these are formed because the system has the tendency to reach a more thermodynamically stable state. This is achieved by reducing the surface free energy by decreasing the surface or interfacial area.

FLOCCULATION

• Particles are weakly bonded, settle rapidly, do not form hard cake, and is easily resuspended. 

  • Particles form loose aggregates or floccules 

  • Particles settle rapidly, but easily resuspended 

  • Particles do not form a cake 

  • After settling, a clear boundary exists between the sediment and the supernatant

  • Upon sedimentation, the flocs, tend to fall together, thus, the liquid above the sediment is clear.

DEFLOCCULATION

• Particles settle slowly and eventually form a sediment in which aggregation occurs within the resultant formation of a hard cake that is difficult to resuspend.

• No clear boundary is formed and the supernatant remains turbid for a longer period of time.