Kinetics of theophylline clearance in gastrointestinal dialysis with charcoal.

The pharmacokinetic response of theophylline following the oral administration of activated charcoal was investigated in rabbits. Rabbits were continuously infused with a theophylline solution at a rate of 2.12 mg/h. At the fourth hour of theophylline infusion, 20 g of activated charcoal was administered by intubation to the rabbit (n = 12). The concentration of theophylline in serum gradually decreased after the charcoal treatment. The magnitude of the change in theophylline concentration induced by charcoal varied among animals. By comparing the steady-state theophylline concentration in the control and treated animals, the total body clearance was found to increase from 94.4 +/- 7.5 to 210 +/- 27 mL/h/kg (mean +/- SE). The rate of change of theophylline concentration in serum following charcoal treatment was fitted with a simulation curve by assuming a stepwise increase in clearance immediately following the charcoal treatment. The results indicated that activated charcoal exerted its maximum effect in increasing theophylline clearance immediately after its administration.