Enteral exsorption of acetaminophen after intravenous injection in rats: influence of activated charcoal on this clearance path.

The fate of acetaminophen after intravenous injection in whole bowel-irrigated rats (n = 40) and the influence of activated charcoal on the kinetics were investigated. After randomization to four groups (n = 10, each group), plasma concentration and the quantities of acetaminophen and metabolites excreted into bile, urine and intestine were determined using an in vivo model with or without orally administered activated charcoal and with or without bile duct cannulation. The cumulative amount of acetaminiphen and metabolites exsorbed into the small intestine within 3.5 hr after intravenous injection was about 20% of dose in the animals with bile duct cannulation and about 7% of dose in the animals without. Correspondingly, about 13% of dose was detected in the externalized bile. Activated charcoal did not influence the amount exsorbed into the small intestine. Terminal half-life in plasma ranged from 35 to 51 min. within the four treatment groups without statistically significant difference (P = 0.152). Correspondingly, the area under the curve did not vary much and ranged between 2.6 and 3.3 g/min./l (P = 0.392). Deposition of acetaminophen and metabolites in liver and kidney after 3.5 hr was marginal and ranged between 0.02% and 0.6% of the dose within all groups. The excretion of acetaminophen and metabolites into urine varied strikingly between 31% and 56% of the dose within all groups and correlated with diuresis. The lack of effect of activated charcoal on the elimination of acetaminophen and metabolites may be due to the small amount of the drug being exsorbed into the intestine or the reduced adsorbent capacity of activated charcoal to acetaminophen and metabolites, which also could be influenced by inadequate luminal stirring.