Predictive stress tests to study the influence of processing procedures on long term stability of supersaturated pharmaceutical o/w creams

Partial coalescence in emulsions is a destabilization mechanism whereby the droplets retain their individual identity but there is a molecular contact between their content. This process can occur under fluctuating temperatures and/or shear stress, which effects the stability and quality of emulsions. In the case of topical drug delivery systems, in particular supersaturated oil-in-water (o/w) creams, the molecular exchange of dissolved drug from one droplet to the other is a critical issue because it can induce drug crystallization and enhance crystal growth. In this work two approaches to address the problem are reported: the stability of the emulsion in relation to (i) shear exposure and (ii) temperature cycling. Some ideas on how this approach can be used to identify critical process parameters and predict long term stability of supersaturated emulsions are discussed.