MS05-P04 Co-crystal forms of the BCS class IV drug sulfamethoxazole Moneerh Alsubaie (School of Chemistry, National University of Ireland Galway, Galway, Ireland) Marwah Aljohani (School of Chemistry, National University of Ireland Galway, Galway, Ireland) Andrea Erxleben (School of Chemistry, National University of Ireland Galway, Galway, Ireland) Patrick McArdle (School of Chemistry,National University of Ireland Galway , Galway, Ireland)email: m.alsubaie1@nuigalway.ieSulfamethoxazole, smz, is an antibiotic which is classified as a Biopharmaceutics Classification System (BCS) class IV, low solubility and low permeability drug. Co-crystal formation has been examined in an attempt to improve solubility. Both ball milling and crystallization from solution have been examined. Ball milling showed that thirteen co-formers gave new crystalline X-ray powder patterns and four gave X-ray amorphous patterns while crystallization from solution gave single crystals of four co-crystals and a salt. The co-formers which gave the co-crystals and the salt have better H-bond acceptors than the sulfonyl oxygens of smz. The 4,4-dipyridyl co-crystal has an interesting high Z’’ structure. It crystallized in space group P1 with four smz and six 4,4’-dipyridyl molecules in the asymmetric unit.The lattice energies of smz and the co-crystals were estimated using the PIXEL program.The dissolution rates of the co-crystals are all lower than smz form I despite the fact that they have lower computed lattice energies than smz form I. It appears that the absence of any hydrogen bond in the smz form I structure with a D…A distance less than 3.2 Å and the presence of stronger hydrogen bonds in the co-crystals with D…A distances close to 2.8 Å is more important in determining dissolution rates than lattice energies.References:

Price, C. P.; Grzesiak, A. L.; Matzger, A. J., J. Am. Chem. Soc. 2005, 127, 5512-5517.

Gavezzotti, A., Zeitschrift für Kristallographie-Crystalline Materials 2005, 220, 499-510.

McArdle, P., J. Appl. Crystallogr. 2017, 50, 320 - 326.

Keywords: Cocrystal