Suspensions, deflocculated preparation

The basic aqueous suspensions were prepared by mixing alumina powder, deflocculant Sokrat 32A together and the rheological parameters were determined. The solid phase content has ranged fiom 60% wt - 85 wt%, deflocculant content 0,2 wt%-0,5 wt% (wt% based on dry solid mass). Based on the dependence of the apparent viscosity q on the deflocculant content added, optimum amount of deflocculant 2,3 wt% was determined (minimum value of... 

The aggregates which frequently arise in aqueous suspension tend to distort the results to a degree substantially exceeding all the other errors. For this reason, a great deal of attention has to be paid to the preparation of samples by ensuring perfect deflocculation of the suspension, preferably by using suitable electrolytes and intensive mechanical agitation however, the latter must not cause break up of the particles. 

Formulation of pharmaceutical suspensions to minimise caking can be achieved by the production of flocculated systems. A flocculate, or floe, is a cluster of particles held together in a loose open stmemre a suspension consisting of particles in this state is termed flocculated (Fig. 7.27). There are various states of flocculation and deflocculation. Unfortunately flocculated systems clear rapidly and the preparation often appears unsightly, so a partially deflocculated formulation is the ideal pharmaceutical. The viscosity of a suspension is obviously affected by flocculation. 

Typical excipients used in parenteral suspensions include surfactants that are used to stabilise emulsions and suspensions as wetting agents (polysorbate 80, poloxamer), as micelle makers for the preparation of solubilisations and to influence the flocculation and deflocculation behaviour of a dispersed system (carmellose sodium, polyvidone). Paren-terally used surfactants in high concentrations are toxic and may cause venous irritation and occasional thrombophlebitis. However, these high concentrations are not necessary to formulate stable parenteral suspensions. 

Sulphamerazine suspensions are in a deflocculated state when prepared with polysorbate 40 [33] (2 %). On standing, the sedimentation volume is around 0.15 and the system is impossible to redisperse after two weeks. Addition of high concentrations of propylene glycol (i.e. greater than 50 %) flocculates the system and renders the suspension dispersible. Propylene glycol dehydrates the surfactant molecules (the cloud point is lowered) hence reducing its stabilizing properties. 

---