Important factors in the size reduction of polymer-stabilized drug particle suspensions using high-pressure homogenization

In recent years, high-pressure homogenization has been used with increasing frequency to reduce the size of pharmaceutical suspensions to the micron, submicron, and nano scales with the goal of increasing the dissolution rate of the drug, and consequently, the in vivo bioavailability. As particle suspensions become smaller in size, increased concentrations of surfactants and stabilizers are required to prevent particle agglomeration. Recently, relatively high concentrations of biocompatible polymers have been used to stabilize suspensions by imparting surface-active steric stability as well as kinetic stability through an increase in suspension viscosity and/or a transition to non-Newtonian rheological properties. While the benefits of stable suspensions are known, little is known about the effect of the high polymer concentration on the actual breakup of the particles in suspension. In this work, designed experiments were used to identify the key parameters that govern the final particle size of a drug suspension following homogenization. In particular, drug loading, operating pressure, and polymer concentration were all found to be statistically significant factors in determining the resulting size of particles in suspension. In addition, it was found that an optimal polymer concentration of 2% (w/w) was required to adequately stabilize the particle suspension while simultaneously avoiding a decrease in homogenizer performance. Concentrations higher than 2% (w/w) resulted in size reduction limitations due to the increased viscosity (>10 cP) and the transition to non-Newtonian behavior.