Determination of norfloxacin by fluorescence in the presence of different antacids: Quantification of analytical interferences

Norfloxacin is a fluorquinolone that can interfere with certain antacids (derivatives of Al and Mg) because its dissolution profiles are dependent on pH. Furthermore, it can form insoluble complexes that modify its absorption and bioavailability. Two sensitive and selective analytical methods using fluorescence (FL) and UV spectrophotometry (UV) have been developed to study the dissolution behaviour in gastric juice of different formulations of norfloxacin in tablets. There are no significant differences when the samples are measured by both methods and their ruggedness in the presence of some excipients is proven. From this, it is concluded that they are effective for this study. When different antacids are added to the dissolution medium, using UV and FL methods with the same samples, totally different dissolution profiles appear. Using FL, it would appear that up to 400% of the amount of norfloxacin in the tablet is released. These profiles are misleading because the uniformity of dosage units was tested before the dissolution studies. It was proven that the antacids dissolved in gastric juice do not produce fluorescence, but cause important analytical interferences with norfloxacin. This may be because their association with Al3+ or Mg2+ forms a new compound. Nevertheless, it is observed that this effect is more important in some antacids (Almagate, Magaldrate). This may be because their ability to deliver Al to the medium is greater.