Journal of Pharmaceutical and Biomedical Analysis 131 (2016) 195–201 Contents lists available at ScienceDirect Journal of Pharmaceutical and Biomedical Analysis journal homepage: www.elsevier.com/locate/jpba Miniaturized X-ray powder diffraction assay (MixRay) for quantitative kinetic analysis of solvent-mediated phase transformations in pharmaceutics Wiebke Kirchmeyer a,b , Olaf Grassmann c , Nicole Wyttenbach d , Jochem Alsenz d , Martin Kuentz a,∗ a University of Applied Sciences and Arts Northwestern Switzerland, Institute of Pharma Technology, Gründenstrasse 40, 4132 Muttenz, Switzerland b University of Basel, Institute of Pharmaceutical Technology, Klingelbergstrasse 50, 4056 Basel, Switzerland c Pharma Technical Development, F. Hoffmann-La Roche Ltd, Grenzacherstrasse 124, 4070 Basel, Switzerland d Roche Pharmaceutical Research & Early Development, Pre-Clinical CMC, Roche Innovation Center Basel, F. Hoffmann-La Roche Ltd, Grenzacherstrasse 124, 4070 Basel, Switzerland a r t i c l e i n f o Article history: Received 25 April 2016 Received in revised form 10 August 2016 Accepted 27 August 2016 Available online 29 August 2016 Keywords: X-ray diffraction Solid state transformation Quantitative analysis Miniaturized assay a b s t r a c t Many pharmaceutical compounds exhibit polymorphism, which may result in solvent-mediated phase transformations. Since the polymorphic form has an essential influence on physicochemical characteris- tics such as solubility or dissolution rate, it is crucial to know the exact polymorphic composition of a drug throughout pharmaceutical development. This study addressed the need to perform quantitative X-ray analysis of polymorphic mixtures on a 96-well scale (MixRay). A calibration of polymorphic mixtures (anhydrate and hydrate) was performed with three model drugs, caffeine, piroxicam, and testosterone, and linear correlations were obtained for all compounds. The MixRay approach for piroxicam was applied to a solubility and residual solid screening assay (SORESOS) to quantify the amount of hydrate and anhy- drate corresponding to kinetic bulk concentrations. Changes in these drug concentrations correlated well with the kinetic changes in the residual solid. The influence of excipients on the solid state and kinetic concentrations of piroxicam was also studied. Excipients strongly affected polymorphic trans- formation kinetics of piroxicam and concentrations after 24 h depended on the excipient used. The new calibration X-ray method combined with bulk concentration analysis provides a valuable tool for both pharmaceutical profiling and early formulation development. © 2016 Elsevier B.V. All rights reserved. 1. Introduction The majority of pharmaceutical compounds exhibit polymor- phism. Since different polymorphic forms of a drug can have different bioavailability and behavior during processing [1,2], it is important to properly characterize the solid form of the drug already early on. Sensitive analytical methods are required espe- cially in case of polymorphic mixtures. A thorough understanding of potential solvent-mediated phase changes is needed for clinical candidates’ selection and for in-process controls to avoid quality issues of the final drug product. An early solid state screening is nowadays typically conducted as part of the pharmaceutical profiling work aiming at the selection ∗ Corresponding author. E-mail address: martin.kuentz@fhnw.ch (M. Kuentz). of the most suitable polymorph of a compound for development [3,4]. Here, not only qualitative information is needed but also a quantification of polymorphic mixtures would be desirable. At an early stage of development, high-throughput (HT) meth- ods for compound characterization (solubility, stability) or testing drug-excipient compatibility are convenient because only a small amount of compound is available. HT-experiments provide the opportunity to test a number of different drugs and excipients, for e.g. solubility determination, in parallel at a miniaturized scale. Parallel testing has also already been reported in the field of drug discovery for the screening of polymorphic forms and for crystal- lization optimization [4,5]. In the field of API-excipient interactions and solubility measurements, some HT-approaches have previ- ously been reported [6–8]. In some of these assays, solid state analysis on a miniaturized scale has already been introduced but only on a qualitative level [6]. Thus there is clearly a need to also quantitatively determine drug solid state changes in a HT-format http://dx.doi.org/10.1016/j.jpba.2016.08.028 0731-7085/© 2016 Elsevier B.V. All rights reserved.