EFFECT OF PARTICLE SIZE ON STABILITY OF SUSPENSION
DIPAK KUMAR DASH
HIMALAYAN PHARMACY INSTITUTE, SIKKIM
Pharmaceutical suspension may be defined as coarse dispersions in which insoluble solids are suspended in a liquid medium. Insoluble solids may have a size range from 10 to 1000 µm.
STABILITY OF SUSPENSION
It is important to understand that suspensions are kinetically stable, but thermodynamically unstable, system.
Physical stability is defined as the condition in which the particles remain uniformly distributed throughout the dispersion without any signs of sedimentation. It is difficult to achieve this condition. Hence the definition can be restated as –if the particles settle they should be easily resuspendable by moderate amount of shaking.
Reference ID: PHARMATUTOR-ART-1093
EFFECT OF PARTICLE SIZE ON STABILITY
When left undisturbed for a long period of time the suspension particles will aggregate, sediment, eventually cake. When a suspension is very well dispersed (i.e., deflocculated), the particles will settle as small individual particles. This settling will be very slow and will result in a low-volume, high-density sediment that may be difficult or impossible to redisperse. When the particles are held together in a loose open structure, the system is said to be in the state of flocculation. Particle size of the active agent plays a key role in the physical stability and bioavailability of the drug product.
The rate of sedimentation, agglomeration, is affected by particle size. The most efficient method of producing small particle size is dry milling. However, wet milling may be desirable for potentially explosive ingredients.
In this system solids are present as individual particles. These system have a shorter shelf life ,but have greater bioavailability when compared to flocculated systems.
In this system particles aggregate themselves by chemical bridging. These folks are light fluffy conglomerates which are held together by weak vanderwall force of attraction.
flocculating agents decreases zeta potential of the suspended charged particle and thus cause aggregation (flock formation) of the particles.
Examples of flocculating agents are:
• Neutral electrolytes such as KCl, NaCl. , Surfactants, Polymeric flocculating agents.
• Sulfate, citrates, phosphates salts
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