Settling in Suspensions, Formulation of Flocculated and Defloculated Suspensions

Settling in Suspensions, Formulation of Flocculated and Defloculated Suspensions

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  Physical Pharmaceutics-II Session 2020-21 Submittedby – Mr. Suyash Jain Department Of Pharmaceutical Sciences Dr. Harisingh Gour Vishwavidyalaya, Sagar (M.P.) Settling in Suspensions, Formulation of Flocculatedand Defloculated Suspensions ( A Central University )
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  Settling in Suspensions •Settlingis a basic phenomenon in suspensions. •All pharmaceutical suspensions has label on the container as “Shake Well before Use”. •Based on the type of suspensions, rate of Settling/Sedimentation may differ.
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  Characteristics of anIdeal Suspensions related to setteling 1. The solid particles should be of such a size that they do not settle rapidly. 2. Even if a sediment is formed, it should not form a hard cake at the bottom of the container. 3. Even if sedimentation occurs, it should be possible to easily redisperse it on moderate shaking.
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  Defloculated Suspension FloculatedSuspension Rate of sedimentation is slow as the size of particals are small. Rate of sedimentation is fast as the size of the formed flocs are large. Particals settle independently and seperately. Particals settle as flocs. The Sedimentation is closely packed and form a hard cake. The Sedimentation is loosely packed and form a hard cake is not formed. Sediment(hard cake) can not be redispersed Sediment is easily redispersed Comparision of partical setteling in Defloculated Suspension and Floculated Suspension
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  The rate ofsedimentation of particles can be expressed by the Stoke's law, using the following formula:- Theory Of Sedimentation
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  Stock's law isapplicable if:- •Particles are spherical; but particles in the suspension are largely irregular. •Particles settle freely and independently. In suspensions containing 0.5 - 2 % (w/v) solid, the particles do not interfere with each other during sedimentation - hence free settling occurs. Sedimentation velocity may be reduced by- • Decrease in particle size • Increase in viscosity • Decrease the density difference
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  How sedimentation velocityis reduced 1. Particle size :- Rate of sediment ∝ (diameter of partical)2 2. Increase in viscosity :- Rate of sediment ∝ 1/(viscosity of medium) 3. Decrease the density difference :- Rate of sediment ∝ (density difference of solid and liquid)
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  Formulation of suspensions
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  Methods of Suspension preperation Precipitation method Organicsolvent pH change Dispersion method
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  Method of preparationscan be subdivided into two broad categories:- 1. Precipitation method: There are two methods:- (A) Organic solvent precipitation:- Water insoluble drugs can be precipitated by dissolving them in water-miscible organic solvents (e.g. alcohol, acetone, propylene glycol and polyethylene glycol) and then adding the organic phase to distilled water under standard conditions produces a suspensionhaving a particle size in the 1 to 5 μm range. (B) Precipitation effected by changing the pH of the medium A drug may be readily soluble at a certain pH and precipitate at another pH. Methods for the preparation
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  2. Dispersion method:- IN this case the powder form of the drug is directly dispersed in the liquid medium. The liquid medium should have good power of wetting the powder. 1. Small scale preparation method 2. Large scale preparation method Prepared by using ball, pebble and colloid mills. Dough mixers, pony mixers and similar apparatus are also employed.