Levels of acetaminophen and its metabolites in mouse tissues after a toxic dose

A high-performance liquid chromatographic method for analysis of acetaminophen and its conjugated metabolites in tissues was developed and used to determine tissue, plasma and urine levels of the drug and its glucuronic acid, sulfate, glutathione, cysteine mercapturic acid conjugates in mice given a 500 mg/kg oral dose of [14C]acetaminophen. Peak levels of unchanged drug occurred at 0.5 hr in plasma, liver and kidney. At the same time, only 30% of the radioactive dose could be recovered from the gastrointestinal tract, indicating rapid absorption of the drug. Peak concentrations of acetaminophen were high in all tissues (1500-2000 nmol/g) and declined with an apparent half-life of 1 hr. Tissue levels of drug conjugates reached a peak at 1 hr and were low relative to unchanged drug for the first 2 hr after the dose. The glucuronic acid and glutathione conjugates reached a similar peak in the liver (325 nmol/g). The glucuronide declined slowly over a 4-hr period, but the glutathione conjugate dropped rapidly between 1 and 2 hr, reflecting depletion of glutathione. Tissue/plasma ratios of metabolites indicated that the glutathione conjugate was concentrated in liver, whereas the cysteine conjugate was concentrated in kidney. Brain levels of unchanged acetaminophen were similar to levels found in other tissues, but conjugates were essentially excluded from the brain reflecting the influence of the blood brain barrier. The results show that certain drug conjugates reach relatively high levels in plasma, liver and kidney, but not brain, after a toxic dose of acetaminophen.