Determination of the adsorption of tramadol hydrochloride by activated charcoal in vitro and in vivo

Although tramadol is one of the most widely used centrally acting analgesic s worldwide, no literature is available regarding adsorption of tramadol HC l powder or tablets (Ultram; 50 mg tramadol HCl per tablet) by activated ch arcoal (AC) for use as potential adjunct treatment of overdose. The present study incorporated a novel combination of in vitro and in vivo methods to investigate this question. Based on a binding curve of tramadol UV absorban ce (UVa,; 225 nm) plotted against the amount of AC, the ratio of amount of tramadol completely adsorbed by AC was 0.05 mg/mg. Also based on UVa, no tr amadol was detected in filtrate of slurries in which up to 62 tablets of Ul tram were mixed with 50 g AC; 4.6% of unbound tramadol was detected when 10 0 tablets of Ultram were mixed with AC. The ratio of amount of tramadol com pletely adsorbed by AC in this test was 0.10. In vivo, co-administration of 0.1 g/ml of AC produced a 13- to 14-fold rightward shift in tramadol's ant inociceptive dose-response curve and a 1.6-fold rightward shift in tramadol 's lethality dose-response curve. (C) 2001 Elsevier Science Inc. All rights reserved.