Effect of dose of charcoal on the absorption of disopyramide, indomethacin and trimethoprim by man

Abstract

The efficacy of various charcoal-to-drug ratios for the absorption of drugs was studied in 6 healthy volunteers and in vitro at two pHs. Disopyramide 200 mg, indomethacin 50 mg and trimethoprim 200 mg were ingested on an empty stomach with 100 ml water. After 5 min the subjects ingested a charcoal suspension in 300 ml — 2.5 g, 10 g, 25 g or 50 g of Norit A, or 10 g of PX-21, or water 300 ml only. Increasing the dose of activated charcoal from 2.5 g to 50 g reduced the gastrointestinal absorption of disopyramide and indomethacin from 30–40% to 3–5%, and that of trimethoprim from 10% to 1% of the respective controls. Disopyramide and trimethoprim were best adsorbed by charcoal in vitro at neutral and indomethacin at acid pH, but saturation of the adsorption capacity was apparent at charcoal-to-drug ratios less than 7.5. Combining the in vitro and in vivo results it can be concluded that the dose of activated charcoal to be given in acute intoxication should be as large as possible, because the drug history is often unknown.