Preparation and Evaluation of Amino Acid Based Salt Forms of Model Zwitterionic Drug Ciprofloxacin

Preparation and Evaluation of Amino Acid Based Salt Forms of Model Zwitterionic Drug Ciprofloxacin Ciprofloxacin (CIP) is a quinolone derivative which is widely used for the treatment of a number of urinary tract infections. It exhibits its antimicrobial activity by inhibiting bacterial DNA gyrase enzyme. BCS classification of CIP is challenging due to the absence of any linear dose proportionality of AUC in humans. Yet, most of the studies classify CIP as a BCS IV (low solubility & low permeability drug) candidate. This study aims at exploiting the zwitterionic nature of CIP and investigates the ability of acidic and basic amino acids to form new salts with the primary aim of improving its solubility. Two salts were prepared using L-glutamic acid and L-aspartic acid as counter ions which resulted in increasing CIP solubility by 2.9x103 and 2.5x103 folds respectively. On the other hand, cationic amino acids namely (L-arginine, L-lysine & L-histidine) failed to form any salts. To investigate the absence of salt formation with the cationic amino acids, the role of inter- and intra molecular interactions between CIP and amino acids on the salt formation was studied using molecular dynamic simulation. Both the experimental and theoretical results revealed that ionic and hydrophobic interactions are essential for salt formation and that the ionic interaction and/or hydrophilic interactions between CIP and amino acids molecules should be greater than hydrophobic interactions between CIP molecules. Future work will study the effect of the salts on the permeability behaviour of CIP across Caco-2 monolayers.