Cocrystals belong to a relatively new class of compounds, which are of special interest in pharmaceutics, as they may serve as alternative drug formulations. Cocrystals may have improved properties, such as the solubility or dissolution rate, in comparison with other crystalline forms of active pharmaceutical ingredients (APIs). Moreover, the production of drugs in the form of cocrystals may be more feasible and provide improved stability.

We used amino acids as co-formers to obtain co-crystals of different APIs. Amino acids are natural to the body, which makes them perfect candidates for cocrystallization of APIs – the drug Spidifen® (Ibuprofen and L-arginine) being the perfect industrial example of the use of an amino acid as a cocrystal co-former. We screened amino acids and amino acid derivatives with S-Naproxen, Levetiracetam, and S-Oxiracetam by liquid-assisted grinding with methanol. The results were analyzed by X-ray powder diffraction. Only S-Naproxen showed positive hits. So far, we succeeded to obtain single crystals for a co-crystal hydrate containing S-Naproxen and D-tryptophan. The structural motifs in that cocrystal are similar to those observed in (1): amino acid molecules form zwitterionic head-to-tail chains, thereby organizing columns, to which S-Naproxen connects via hydrogen bonds. It thus seems that zwitterionic amino acids can be successfully used as cocrystal coformers with carboxylic acids, but fail when dealing with amides, or alcohol compounds. These results should be definitely taken into account when developing new solid forms of APIs.

 1. Tilborg A, Springuel G, Norberg B, Wouters J, Leyssens T. CrystEngComm. 2013.

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1. Does Chirality Influence the Tendency of Co-crystal Formation ?