Complexes of Ciprofloxacin with Metal Ions Contained in Antacid Drugs

Abstract

Simultaneous administration of antacids containing magnesium or aluminium and ciprofloxacin or other qui-nolones decreases the gastrointestinal absorption of those antibacterial agents. Current speculation about the mechanism of this interaction has focused on drug-cation chelation. The present study was designed to detect the protonation in solutions and the formation of the complex species at the pH levels typical of the gastro-intesti-nal tract. It involves the study of ciprofloxacin in aqueous solutions containing Al³⁺ and (or) Mg ²⁺ by combining the results of potentiometric and spectro-scopic (¹H nuclear magnetic resonance) 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 equilibrium model including complex species MHL, MLOH (where H₂L denotes ciprofloxacin and M is Al ³⁺ or Mg ²⁺); their formation constants are given.