Question

a) Explain the terms “flocculated” and “deflocculated” systems as applicable to pharmaceutical suspensions.

b) Describe the role of two excipients that are added specifically to suspension formulations. Illustrate your answer with examples.

c) Derjaguin-Landau-Verwey-Overbeek (DLVO) theory predicts the stability of lyophobic colloidal systems. Explain the key elements of DLVO theory and how this theory can assist in the preparation of a stable suspension.

Answer 1

a) Pharmaceutical suspensions are biphasic dispersions having insoluble drug, dispersed in the solvent.

When the particulate matters are uniformly distributed and deaggregated in the system ther are reffered as deflloculated suspension. The deffloculated agents are mixed during preparation of such suspension. The cake formed due to settling is hard in this case.

On the other hand if the pariculate matters are aggregated to form agglomerated mass then these are reffered as flocculated suspension, Although thse flocules rae airy and spongy having the property to get redispersed on shaking. The flocculating agenyts are used in the preparation of such use types of suspenstion. The cake formed due to settling is not hard in this case.

b) The defloculating agents and thickening agents are used in the formulation of the suspensions.Suspensding/thickening agents example gum tragacanth & methylcellulose.

Defloculating agents Example: KCl, NaCl and Surfactants,

c) DLVO theory predict the aggregation of aqueous dispersion like suspension during the stability testing. It also affects the settling of the particulate matters in the suspension under the influence of   electrostatic repulsion as well as Van der Waals attraction in the form of double layer of counterions. DLVO theory explains the stablity of the pharmaceutical suspensions in therms of the zeta potencial including the double layer concepts on the interphase.

Particles having the similar charges get repel to each other while particle of opposite charges get attracted to each other. Thus on the basis of such electrostatic DLVO theory the stability of pharmaceutical suspensions is expressed.