Effects of size and frequency of oral doses of charcoal on theophylline clearance.

The effect of size and frequency of oral doses of activated charcoal on theophylline kinetics was studied. Six fasting, healthy men received intravenous infusions of aminophylline (6 mg/kg) over 1 hr, followed by either no activated charcoal as a control, 5 gm activated charcoal every 2 hr for 6 doses, 10 gm every 2 hr for 6 doses, 10 gm every hr for 12 doses, 20 gm every 2 hr for 6 doses, or 40 gm every 4 hr for 3 doses. Five grams every 2 hr decreased serum theophylline t 1/2 from the control of 9.1 +/- 0.7 to 5.6 +/- 0.4 (SE) hr and decreased the AUC from the control of 123 +/- 11 to 79 +/- 6 mg X hr/l. The regimen of 20 gm every 2 hr further decreased theophylline t 1/2 to 4.3 +/- 0.4 hr and decreased AUC to 62 +/- 6 mg X hr/l. When a 120-gm dose of activated charcoal was given as a regimen of 40 gm every 4 hr or as a regimen of 10 gm every hr, there were small differences in serum theophylline t 1/2 (5.4 +/- 0.3 and 4.3 +/- 0.2 hr) and in AUC (73 +/- 5 and 60 +/- 4 mg X hr/l). Repeated small doses of oral activated charcoal enhanced the total body clearance of theophylline, and larger doses induced a relatively small further increase. There was little difference between the effects of the same total dose every 4 hr vs every hour.