COMPLEXES OF CIPROFLOXACIN WITH METAL-IONS CONTAINED IN ANTACID DRUGS

Simultaneous administration of antacids containing magnesium or alumin ium and ciprofloxacin or other quinolones decreases the gastrointestin al absorption of those antibacterial agents. Current speculation about the mechanism of this interaction has focused on drug-cation chelatio n. The present study was designed to detect the protonation in solutio ns and the formation of the complex species at the pH levels typical o f the gastrointestinal tract. It involves the study of ciprofloxacin i n aqueous solutions containing Al3+ and (or) Mg2+ by combining the res ults of potentiometric and spectroscopic (H-1 nuclear magnetic resonan ce) techniques. Calculations were only performed for data in the range 4.5 < pH < 5.5 (pH levels typical of gastrointestinal tract) and the results of both methods are made self-consistent, assuming an equilibr ium model including complex species MHL, MLOH (where H(2)L denotes cip rofloxacin and M is Al3+ or Mg2+); their formation constants are given .