Improving the API dissolution rate during pharmaceutical hot-melt extrusion I: Effect of the API particle size, and the co-rotating, twin-screw extruder screw configuration on the API dissolution rate

• The effect of API particle size and extruder screw configuration was investigated on the dissolution of the API during hot melt extrusion.
• Reducing the API particle size and selecting the appropriate screw configuration markedly improves the dissolution of API.
• Upon milling of API, the flowability of the physical mixture significantly improves compared to the physical mixture containing the original API
• Accelerating the API dissolution in these ways can be further exploited to reduce the processing temperature and residence time of the API during extrusion, thus, minimizing the risk for thermal degradation of the API.
• Dry coating of the excipient particles by the milled API particles can increase the flowability of binary pharmaceutical formulations without the need to add a third component as a “glidant”.

The dissolution rate of the active pharmaceutical ingredients in pharmaceutical hot-melt extrusion is the most critical elementary step during the extrusion of amorphous solid solutions – total dissolution has to be achieved within the short residence time in the extruder. Dissolution and dissolution rates are affected by process, material and equipment variables. In this work, we examine the effect of one of the material variables and one of the equipment variables, namely, the API particle size and extruder screw configuration on the API dissolution rate, in a co-rotating, twin-screw extruder. By rapidly removing the extruder screws from the barrel after achieving a steady state, we collected samples along the length of the extruder screws that were characterized by polarized optical microscopy (POM) and differential scanning calorimetry (DSC) to determine the amount of undissolved API. Analyses of samples indicate that reduction of particle size of the API and appropriate selection of screw design can markedly improve the dissolution rate of the API during extrusion. In addition, angle of repose measurements and light microscopy images show that the reduction of particle size of the API can improve the flowability of the physical mixture feed and the adhesiveness between its components, respectively, through dry coating of the polymer particles by the API particles.

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