The physicochemical and antibacterial properties of ciprofloxacin-Mg2+ complex

Co-administration of quinolone antibiotics with cation-containing medicaments such as, antacids has been reported to influence the overall bioavailability leading to subtherapeutic plasma concentrations of these antibiotics in humans.

The present work was designed to evaluate the binding constant, binding molar ratio, influence of temperature on the binding constant of ciprofloxacin-Mg2+ and to determine the antimicrobial activity of ciprofloxacin and ciprofloxacin-Mg2+.

Job's method of continuous variation and Bonesi-Hildebrand equation were adopted to determine the molar ratio and stability constant respectively. The antibacterial activity was determined by the Agar diffusion method.

A complexation molar ratio of 1:1 was obtained for ciprofloxacin-Mg2+ complex. The stability constants were 3.59 and 3.50 at 25 degrees C and 60 degrees C respectively. There was a significant difference between the zones of inhibition of ciprofloxacin-Mg2+ complex and that of ciprofloxacin alone against E. coli, P. aeruginosa, and S. aureus (p < 0.05). This difference showed that the complex formed was not as active as ciprofloxacin.

The present studies have shown that ciprofloxacin readily complex with Mg2+ and that the stability constant was temperature dependent. The antibacterial activity of ciprofloxacin was markedly reduced in the presence of Mg2+. Concomitant administration of ciprofloxacin with Mg2. containing medicaments should be avoided to prevent resistance.