Absorption of sodium pentobarbital by three types of activated charcoal

The in vitro adsorption of sodium pentobarbital by activated charcoal (USP), Darco G-60 and SuperChar was studied. Various solutions of sodium pentobarbital, ranging in concentration from 2.5 to 10 mg/ml (pH = 9), were prepared in distilled water. Radiolabeled (14C) sodium pentobarbital was added to serve as a concentration marker. Two millimeters of each solution was added to from 5 to 350 mg of each charcoal in a test tube. The resulting charcoal-drug slurries were mixed thoroughly and incubated at 37 C for 10 min. Analysis of supernatant allowed calculation of percentage of drug bound. Plots of percentage of drug bound vs log quantity of charcoal necessary to bind 50% of the drug (B-50) were constructed. B-50 was lowest for SuperChar (indicating highest binding capacity), followed by USP and Darco G-60 activated charcoals. In a second series of experiments, drug adsorption was determined at various pH's, or when sodium pentobarbital was dissolved in various volumes of distilled water. Adsorption of the drug from solutions buffered at pH 8.1, 9, 9.7, 11 and 12 did not differ from adsorption in aqueous solution. Adsorption of sodium pentobarbital by 50 or 100 mg of each charcoal did not change when 5 mg of the drug was dissolved in 1, 2, 4, 6, 8 or 10 ml of water. The results suggest that sodium pentobarbital is most readily adsorbed by SuperChar under all conditions studied, followed by USP and Darco G-60 activated charcoals. Changes in pH, or in the initial mixture volume, did not influence the degree of drug adsorption to activated charcoal.