Activated charcoal alone and followed by whole-bowel irrigation in preventing the absorption of sustained-release drugs.

OBJECTIVE: Our objective was to study the effect of activated charcoal on the absorption of sustained-release drugs ingested 1 hour earlier and to examine whether whole-bowel irrigation affects the efficacy of charcoal.

METHODS: In this randomized, 3-phase crossover study, 9 healthy subjects received, at the same time, 200 mg carbamazepine, 200 mg theophylline, and 120 mg verapamil. All drugs were given as sustained-release tablets. One hour after taking the tablets, the subjects were assigned to one of the following treatments: 25 g activated charcoal as a suspension, 25 g activated charcoal as a suspension followed by whole-bowel irrigation with polyethylene glycol (PEG) electrolyte lavage solution, or 200 mL water (control). The absorption of the drugs was characterized by using the area under the plasma drug concentration-time curve from time zero to 24 hours [AUC(0-24)], peak plasma concentration (C(max)), C(max) minus the plasma concentration at 1 hour (C(Delta)), and time to peak (t(max)).

RESULTS: Activated charcoal alone given 1 hour after drug intake significantly (P <.001) reduced the absorption [AUC(0-24)] of all 3 drugs (by 62%-75%). Also the C(max) and C(Delta) values of these drugs were significantly reduced by charcoal alone. Whole-bowel irrigation did not increase significantly the effect of charcoal on any absorption parameters of the 3 drugs studied. On the contrary, whole-bowel irrigation significantly (P <.01) decreased the efficacy of charcoal with respect to carbamazepine.

CONCLUSIONS: Activated charcoal alone given 1 hour after intake of sustained-release drugs was effective in preventing the absorption of all 3 drugs studied. Whole-bowel irrigation may even decrease the efficacy of charcoal if the drug is well adsorbable onto charcoal. However, our study was performed with therapeutic drug doses only. In overdoses their possible effects on gastrointestinal motility may modify the efficacy of decontamination methods.