ABSTRACT
A classical emulsion formulation based on petrolatum and mineral oil as the internal phase with emulsifier wax as a typical topical emulsion cream was investigated for the effect of process parameters on drug product quality and performance attributes. The Initial Design of Experiment (DoE) suggested that an oil phase above 15%, coupled with less than 10% emulsifying wax, resulted in less stable emulsions. Different processing parameters such as homogenization speed, duration, cooling rate, and final temperature showed minimal influence on properties and failed to improve stability. The final DoE suggested that the optimal emulsion stability was achieved by introducing a holding period midway through the cooling stage after solvent addition. Within the studied holding temperature range (25-35 °C), a higher holding temperature correlated with increased emulsion stability. However, the application of shear during the holding period, using a paddle mixer, adversely affected stability by disrupting the emulsion microstructure. IVRT studies revealed that the release of lidocaine was higher in the most stable emulsion produced at a holding temperature of 35 °C compared to the least stable emulsion produced at a holding temperature of 25 °C. This suggests that a holding temperature of 35 °C improves both the stability and active release performance. It appears that a slightly higher holding temperature, 35 °C, allows a more flexible and stable emulsifying agent film around the droplets facilitating stabilization of the emulsion. This study offers valuable insights into the relationship between process parameters at various stages of manufacture, microstructure, and various quality attributes of emulsion cream systems. The knowledge gained will facilitate improved design and optimization of robust manufacturing processes, ensuring the production of the formulations with the desired critical quality attributes.
ABSTRACT
The manufacturing process for ointments typically involves a series of heating, cooling, and mixing steps. Precise control of the level of mixing through homogenization and the cooling rate, as well as temperature at different stages, is important in delivering ointments with the desired quality attributes, stability, and performance. In this work, we investigated the influence of typical plant processing conditions on the microstructure, stability, and sensorial properties of a model ointment system through a Design of Experiments (DoE) approach. Homogenization speed at the cooling stage after the addition of the solvent (propylene glycol, PG) was found to be the critical processing parameter that affects stability and the rheological and sensorial properties of the ointment. A lower PG addition temperature was also found to be beneficial. The stabilization of the ointment at a lower PG addition temperature was hypothesized to be due to more effective encapsulation by crystallizing mono- and diglycerides at the lower temperature. The in vitro release profiles were found to be not influenced by the processing parameters, suggesting that for the ointment platform studied, processing affects the microstructure, but the effects do not translate into the release profile, a key performance indicator. Our systematic study represents a Quality-by-Design (QbD) approach to the design of a robust manufacturing process for delivering stable ointments with the desired performance attributes and properties.
