The ability of activated charcoal (AC) to adsorb toxicologically important agents in the gastrointestinal tract, and thus prevent their adsorption, has been acknowledged for over a century.1) However, it was not until the 1960s that AC gained more general use in the management of acute intoxication. Oral AC effectively prevents the absorption of most drugs present in the stomach at the time of charcoal administration; however, it does not inhibit the absorption of all toxicologically important agents.2)The primary rationale for the use of cathartics together with AC in the management of acute poisoning is the belief that these agents reduce the absorption of a poison by decreasing the time the poison or the poison-charcoal complex remains in the gut. Also, cathartics have been administered with AC to reduce the risk of constipation, impaction and quantity of activated charcoal needed, and to improve the taste of AC, thereby reducing its grittiness and making it more palatable. However, not all cathartics achieve this reduction in time and quantity antidotal efficacy of AC on all poisoning agents. Several in vivo and in vitro studies have shown different cathartics which either produce no significant change in time and quantity of AC necessary for adsorption, give only a modest beneficial effect or even reduce the adsorptive capacity of AC. [3][4][5][6] Rifampicin is an antibacterial agent used mainly in the treatment of tuberculosis. It is a potent inducer of cytochrome P-450 (CYP) enzymes and thus causes many drug interactions.7) At the usual dose of 600 mg once daily, rifampicin is generally well tolerated, but hepatotoxicity is a potential adverse effect, and several such cases have been reported. 8,9) The aim of this study, therefore, was to investigate the effect of sodium chloride and sodium citrate on the in vitro adsorption of therapeutic and simulated toxic doses of rifampicin to AC.
MATERIALS AND METHODSActivated charcoal (Ultracarbon, Merck), sodium chloride and sodium citrate (reagent grade) (BDH, England) and rifampicin (IDA, Malta) were used in this study. 50, 100, 200, 400 and 500 mg of AC were placed in test tubes. Several solutions of rifampicin in 2.5, 5, 10, 50 and 100 mg/ml were prepared in distilled water, and 5ml of each solution was added to each adsorbent tube. The resulting rifampicin-charcoal slurries were vortex mixed for 30 s, incubated in a water bath shaker for 30 min at 37°C, and centrifuged at 3000 rpm for 5 min. Rifampicin was then determined on the clear supernatant using a Jenway Colorimeter 6400 at a wavelength of 320 nm.Another experiment was carried out to determine the effects of sodium chloride and sodium citrate on the ability of AC to adsorb rifampicin. 5 ml of solutions containing 7.5 mg/ml each of sodium chloride and sodium citrate with 2.5, 5, 10, 50 and 100 mg/ml rifampicin, prepared using a solution of the cathartics as the solvent for rifampicin, were added to test tubes containing 50, 100, 200, 400 and 800 mg AC. The tubes were vortex mixed, incubated, centrifuged...