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Bioavailability of orally administered fluoroquinolones has been shown to be hampered by factors that reduce gastro-intestinal absorption of the drugs. These factors include the presence of metallic drugs or agents which result in the formation of drug-cationic chelate complexes in the gut which make the fluoroquinolone molecules unavailable for absorption. Similarly, concurrent administration of some drugs alongside adsorbents like activated charcoal reduces the amount of the drug that could be absorbed from the gut due to binding of the drug molecules to the adsorbent. Binding capacities of adsorbents have also been known to be dependent on their surface polarity and surface area. Concomitant administration of fluoroquinolones with adsorbents would result in the binding of the fluoroquinolones on the adsorbents and thereby making the adsorbed fluoroquinolones to be unavailable in the right proportion required to effect the desired antibacterial activity. The ensuing therapeutic failure therefore, is of grave concern to the patient who would not derive value for his money and in some critical circumstances suffer an irreparable damage to his health. However, the phenomenon is of great importance in the management of cases of accidental ingestion and over dosage involving fluoroquinolones. The aim of this work therefore, is to evaluate the extent to which adsorption of fluoroquinolones viz ciprofloxacin, ofloxacin and norfloxacin could be affected by common adsorbents such as activated charcoal (carbon), bentonite and kaolin. The experimental conditions were simulated to mimic normal human Gastro-Intestinal Tract (GIT) environment by using 0.1M hydrochloric acid (HCl) at 37oC and constant shaking. Definite amounts of fluoroquinolones were treated with graded amounts of adsorbents ix Over a period of time during which samples were taken at regular intervals to determine the drug concentrations which were measured by Ultraviolet/Visible (UV) absorption of the samples at wavelengths of their maximum absorption.
The results obtained showed that activated carbon and bentonite exhibited a high degree of adsorption to the three fluoroquinolones while kaolin showed poor binding capacities to the three compounds. The result was evaluated in accordance with the Langmuir adsorption isotherm in line with similar works earlier carried out. The implication of these findings is two-fold: 1. The high binding capacities exhibited by activated carbon and bentonite to ciprofloxacin, ofloxacin and norfloxacin supported the view that the two adsorbents are good antidotes in cases of accidental ingestion of these antibacterial agents. However, these adsorbents should be avoided during fluoroquinolone therapy as they will bind the fluoroquinolones and therefore lead to therapeutic failure. 2. The poor binding capacities exhibited by kaolin to ciprofloxacin, ofloxacin and norfloxacin reduces the apprehension about therapeutic failure during concurrent administration with the fluoroquinolones.
