Abstract
Pharmacokinetics on the formation and the excretion of the conjugates following rapid intravenous injection of N-acetyl-p-aminophenol (NAPA) was investigated in rabbits. In conflict with the assumption made by Nelson and Morioka in man that each excretion of the NAPA conjugates (glucuronide and sulfate) after dosage of NAPA would be rate-limited by each formation step, it was confirmed in rabbits that the formation step of the conjugates progressed much more rapidly than the subsequent excretion step. Furthermore, making a simplification that the two NAPA conjugates might be treated single since the glucuronide is predominant, the model fitting to the blood levels of free NAPA and the conjugate and the excreted amounts of the conjugate in the urine was elucidated, which consisted of a three-step consecutive first order process, the first step of which was the formation of the conjugate, the second the transfer of the conjugate from the blood to a hypothetical compartment, and the third urinary excretion of the conjugate through the intervenient compartment and two competitive first order processes, respectively, for the second step of the three-step consecutive process mentioned above and the direct urinary excretion of the conjugate from the blood.
