Effects of magnesium citrate and clidinium bromide on the excretion of activated charcoal in normal subjects

The efficacy of cathartics in shortening the gastrointestinal transit time of activate charcoal (AC) in the presence of drugs that alter gastrointestinal motility has not been determined. We evaluated the effects of magnesium citrate (MC) on the excretion of activated charcoal in healthy volunteers alone and with concurrent administration of the anticholinergic drug clidinium bromide. Forty subjects were randomized to clidinium bromide 5 mg or placebo capsule (PC), followed by activated charcoal 15 g and magnesium citrate or a placebo liquid (PL). The onset and duration of excretion of activated charcoal were noted. Mean onset times for activated charcoal were: group I (CB, MC) 4.5 +/- 2.1 h; group II (CB, PL) 17.0 +/- 10.0 h; group III (PC, MC) 6.3 +/- 5.8 h; and group IV (PC, PL) 20.6 +/- 8.4 h. The onset of excretion of activated charcoal was statistically different in both magnesium citrate groups as compared with the placebo liquid groups. The duration of activated charcoal in the stool was similar among the groups. The addition of clidinium bromide did not appear to affect gastrointestinal transit time. These results support previous studies of the effects of cathartics on the excretion of activated charcoal, and suggest that cathartic efficacy is not inhibited by anticholinergic drugs when used in therapeutic doses.