Pharmaceutical salts of ciprofloxacin with dicarboxylic acids.

New salts of antibiotic drug ciprofloxacin (CIP) with pharmaceutically acceptable maleic (Mlt), fumaric (Fum) and adipic (Adp) acids were obtained and their crystal structures were determined. The crystal lattices of the fumarate and adipate salts were found to accommodate the water molecules, while the maleate salt was anhydrous. The dehydration and melting processes were analyzed by means of differential scanning calorimetry and thermogravimetric analysis. Solubility and intrinsic dissolution rates of the salts were measured in pharmaceutically relevant buffer solutions with pH 1.2 and pH 6.8. Under acidic conditions, the salts were found to be less soluble than the parent form of drug, while the [CIP+Fum+H2O] and [CIP+Mlt] solids showed enhanced dissolution rate when compared to a commercially available ciprofloxacin hydrochloride hydrate. In the pH 6.8 solution, all the salts demonstrated solubility improvement and faster dissolution rate with respect to pure CIP.