Absorption inhibition and enhancement of elimination of sustained-release theophylline tablets by oral activated charcoal.

The effect of orally administered activated charcoal (OAC) on the first 12 hours of absorption and elimination of sustained-release theophylline tablets (SRT) was investigated in 20 normal children ages 8 to 18 years. The theophylline absorption-elimination characteristic of all subjects was determined after ingestion of 10 mg/kg SRT. Blood for theophylline was sampled at 0, two, four, six, eight, ten, 12, and 24 hours. After a 72-hour theophylline washout period, the subjects were assigned randomly to one of four study groups and received 10 mg/kg SRT. OAC then was given as a single dose one hour later to Group 1 subjects. Group 2 subjects took four doses of OAC at three-hour intervals beginning at one hour after SRT dosing. Group 3 subjects also received four doses of OAC at three-hour intervals with the first dose given three hours after SRT; Group 4 subjects received three doses at similar intervals with the first dose administered six hours after SRT dosing. OAC administration reduced the 12-hour area under the concentration time curve for theophylline (AUC) by 61% in Group 1, by 68% in Group 2, by 37% in Group 3, and by 18% in Group 4. The differences in AUC between treated and untreated subjects were significant at P less than .01 for Group 1, at P less than .001 for Group 2, at P less than .02 for Group 3, and not significant for Group 4. These data indicate that early OAC administration can inhibit SRT absorption significantly and enhance elimination of previously absorbed theophylline.