The physicochemical and antibacterial properties of ciprofloxacin-Mg2+ complex.

Purpose: 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.

Objectives Of The Study: 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+.

Methods: 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.

Results: 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.

Conclusion: 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.