Recent advances in in situ measurement technology and automation of batch crystallizers have enabled the development of batch crystallization recipes in which the desired supersaturation profile is followed by feedback control. This paper describes a new approach for following supersaturation setpoints for antisolvent crystallizations that is easy to implement for the tried crystallization. Simulations and application to a proprietary drug compound demonstrate how this combination of automation and in process measurements enables the rapid development of batch crystallization processes in the pharmaceutical industry.

In situ Raman spectroscopy was used to determine the rate of polymorph turnover for MK-A, a multipolymorphic compound in development at Merck Research Laboratories. The known crystal forms of MK-A include four anhydrous polymorphs, two hydrates, and numerous solvates. The penultimate and pure steps of this process involve a coupling reaction to generate a mixture of crystal forms followed by turnover to the desired polymorph, form A. This paper summarizes experiments to measure the kinetics of polymorph turnover from all relevant MK-A crystal forms to form A. Additionally, the turnover kinetics for polymorph reversion from form A to undesired forms were measured under simulated process upset conditions. The use of thermodynamic data to establish process boundaries and kinetic data to establish process time cycles resulted in the definition of a highly robust, cycle time efficient slurry turnover process to produce form A from any combination of other MK-A crystal forms.

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