In vitro study on fluoxetine adsorption onto charcoal using potentiometry

This in vitro investigation was performed to study the adsorption rate cons tant as well as the adsorption characteristics of fluoxetine (F) to activat ed charcoal and its commercial formulation Carbomix powder in simulated gas tric (pH 1.2) fluid environment. Ion-selective electrode (ISE) potentiometr y, based on the selective, direct and continuous monitoring of F with an F- ISE constructed in our laboratory was used. The method used in the kinetic experiments consists of the rapid addition of a slurry containing the charc oal into the drug solution under stirring and continuous recording of the F -ISE potential until the establishment of equilibrium. The free ionized dru g concentration at appropriate time intervals was calculated from the recor ded adsorption curve and the apparent adsorption rate constant was estimate d assuming pseudo first order kinetics. Within run R.S.D. of the estimates ranged from 0.24 to 11.5%, while between run R.S.D. (n=3-4) ranged from 0.9 0 to 13.8%. A linear relationship was found between the apparent adsorption rate constants and the amount of charcoal used with slopes (+/-S.D.) for a ctivated charcoal and Carbomix equal to 1.14(+/-0.21) and 0.146(+/-0.009) s (-1) g(-1), respectively. Successive additions of microvolumes of F solutio n were made into a charcoal slurry with measurement of the F-ISE potential at equilibrium. The maximum adsorption capacity values (+/-S.D.) of activat ed charcoal and Carbomix were 254.8+/-1.8 and 405+/-41 mg/g, respectively w hile the affinity constant values (+/-S.D.) were 45.6+/-2.2 and 55.5+/-2.91 /g, respectively. The adsorption of F to charcoals was rapid and for amount s of charcoal 10 times greater than the amount of the drug, 95% of F was ad sorbed within the first 5 min. Relative to the toxic and lethal doses in ca ses of F intoxications, both types of charcoals tested adsorbed effectively F at gastric pH. Carbomix can be considered as appropriate charcoal formul ation for medical treatment in cases of F poisoning. (C) 2001 Elsevier Scie nce B.V. All rights reserved.