Processing-induced-transformations (PITs) during direct compression: impact of compression speeds on phase transition of caffeine

Abstract

For pharmaceutical industry, understanding solid-phase transition of the active pharmaceutical ingredient (API) induced by the manufacturing process is a key issue. Caffeine was chosen as a model API since it exhibits a polymorphic transformation during tableting. This study investigated the impact of the compression speed on the phase transition of anhydrous Form I (CFI) into Form II. Tablets were made from pure CFI and binary mixtures of CFI/microcrystalline cellulose, with an electric press well instrumented at three different compression speeds (50, 500 and 4500 mm min⁻¹). For each velocity of the mobile punch studied, tablets made from three compression pressures (50, 100 and 200 MPa) were analyzed. The determination of the CFI transition degree was performed using a Differential Scanning Calorimetry (DSC). The CFI transition degree was monitored during three months in order to obtain the transformation profile of the API in tablets and in uncompressed powder. The modeling of the profile with a stretched exponential kinetic law (Johnson–Mehl–Avrami model) was used for the identification of the transition mechanism. The direct compression process triggered the polymorphic transformation in tablet when a sufficient compression pressure is applied. The velocity of the punch did neither impact the transition degree just after compression nor the transformation profile. The transition mechanism remained driven by nucleation for several operating conditions. Consequently, the punch velocity is not a decisive process parameter for avoiding such phase transition in tableting. As already observed, the compression pressure did not influence the transition whatever the compression speed and the velocity.

Keywords:

• Caffeine
• direct compression
• polymorphic transformation
• process parameters
• processing induced transition
• tableting

Acknowledgements

The support of the Ministère de l’Enseignement Supérieur et de la Recherche is gratefully acknowledged. We would like to thank Medel’Pharm, especially T. Ménard, G. Tardy and B. Villa as well as the technician G. Conod-Nardi B. Ponsard and O. Pollet for their technical support. We also wish to thank the IVTV platform (ANR-10-EQPX-06–01).

Disclosure statement

The authors report no conflicts of interest. Only authors are responsible for the content and writing of this paper.