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Abstract
1. After administration to mice of a hepatotoxic dose of paracetamol (400 mg/kg body wt, p.o.) peak plasma concentrations of the drug and its glucuronide were ∼900uM around one hour. Corresponding levels of the sulphate, mercapturate and cysteine conjugates were ∼100, 35 and 20uM, respectively.
2. Urinary excretion accounted for 55% of the administered drug 31 h after dosing. Of this total, 64.7% was paracetamol glucuronide, 17.9% paracetamol cysteine, 10.4% paracetamol sulphate, 0.5% paracetamol mercapturate and 6.5% unchanged drug.
3. One hour after acute ethanol administration (3g/kg, p.o., concomitantly with paracetamol) plasma levels of the glucuronide, cysteine and mercapturate conjugates were decreased by ∼50%. There were reductions in the urinary excretion of the glucuronide (-13%) and cysteine conjugates (-24%), but increases in the amounts of mercapturate (+52%), sulphate +11%) and unchanged drug (+81%).
4. Chronic ethanol ingestion (15 g/kg per d for 28 d) caused a transient initial increase in plasma paracetamol cysteine (+32%) and mercapturate (+41%) concentrations, but the only substantial change in urinary excretion was a 29% increase in the amount of paracetamol glucuronide.
5. After chronic ethanol consumption, acute ethanol administration had a transient inhibitory effect on paracetamol mono-oxygenation, but glucuronidation was unaffected (as judged by plasma concentrations). Only paracetamol mercapturate excretion was substantially affected (+64%)