Steric Stabilization of Suspensions

Introduction The vast majority of work on pharmaceutical suspensions is concerned with the electrical stabilization of such systems, incorporating the 0LV0 theory of colloid science to account for the suspensions characteristics observed. Stabilization of particles, produced by the adsorption of polymers at the solid-liquid interface, has not been extensively investigated in the area of pharmaceutical suspensions. It is only recently that theories describing this “steric stabilization” have been (2) introduced and these may be used only with certain restrictions Steric stabilization has one major advantage over electrostatic stabilization in that it is relatively insensitive to the presence of added electrolytes. The addition of ionic exclpients such as colourings, flavourings, buffers and preservatives must be taken into account when formulating a dispersion where stabilization is by electrostatic means alone. Possible leaching of ionic species from glass containers may also cause unwanted changes in suspension appearance and redispersibility. Stabilization of particles through the adsorption of polymers avoids this problem as the steric effect is independent of added electrolyte and high ionic strengths are usually required before the solution properties of nonionic polymers are affected.