The effects of hepatic and renal damage on paracetamol metabolism and excretion following overdosage. A pharmacokinetic study

1. The kinetics of paracetamol metabolism and excretion were studied in 41 patients following overdosage. Acute hepatic necrosis developed in 23 patients and in 3 of these acute renal failure also occurred. Two patients died in hepatic failure.2. Paracetamol metabolism was impaired in the patients with liver damage. The plasma half-life of the unchanged drug was significantly prolonged, and the ratio of the plasma concentrations of unchanged to conjugated paracetamol was significantly higher than in the patients without liver damage.3. Paracetamol and its conjugates were rapidly excreted in the urine. However, excretion was slower in patients with liver damage and a higher proportion was excreted unchanged.4. The renal clearance of unchanged (but not conjugated) paracetamol was related to the urine flow rate. However, forced diuresis is of no practical value and is contraindicated on clinical grounds. There was no correlation between urine pH and clearance of unchanged or conjugated drug.5. In patients with hepatic necrosis there was a marked decrease in the overall elimination rate constant which could be accounted for by decreased metabolite formation. Except in patients with acute renal failure, the urinary excretion rate constants were similar to those observed in patients without liver damage.

Reduction of absorption of paracetamol by activated charcoal and cholestyramine: a possible therapeutic measure

The absorption of an oral 2-g dose of paracetamol was markedly reduced by the simultaneous oral administration of either activated charcoal or cholestyramine but was only slightly reduced when the adsorbents were given 60 minutes after the paracetamol. Since the absorption of a larger dose of the drug will probably be slow, the administration of adsorbents may be of value even when delayed several hours.

Lysozymuria and acute disorders of renal function

On the assumption that increased urinary lysozyme concentration (;lysozymuria') indicates tubular proteinuria and therefore impaired tubular function, urinary lysozyme has been estimated in acute disorders where transient disturbances of renal function might be expected, in cases diagnosed clinically as extrarenal uraemia, and in a few examples of acute renal disease. Reversible lysozymuria occurred with hypokalaemia, postoperative ;collapse', electrolyte depletion, severe extrarenal infection, acute pyelonephritis, the nephrotic syndrome, after a few apparently uncomplicated surgical operations, and very transiently after ventricular fibrillation abolished by DC shock. There was no lysozymuria with severe uraemic heart failure, aspirin and paracetamol poisoning, or severe jaundice, nor in two cases of acute glomerulonephritis. Although lysozymuria may occasionally be useful in the clinical diagnosis of acutely disordered renal function, the results suggest that its value is limited; on the other hand, they have provided information on renal pathophysiology in acute disease.

Potentiation by previous drug therapy of hepatotoxicity following paracetamol overdosage

Patients developing hepatic necrosis following intoxication with paracetamol were classified as either ‘potentially induced’ or ‘non-induced’ according to their consumption during the previous 3 weeks of drugs likely to cause liver microsomal enzyme induction. Despite uncontrolled differences between the two groups the ‘potentially induced’ group developed statistically significantly more severe hepatic necrosis than the ‘non-induced’ patients. The greater severity of liver damage in the former group was accompanied by a higher incidence of death and acute renal failure. This is consistent with the observation that paracetamol-induced hepatic necrosis in animals is mediated by toxic intermediate metabolites.