Abnormal drug metabolism after barbiturate and paracetamol overdose

Drug-metabolizing capacity has been assessed by serial measurements of the plasma antipyrine half life in 11 patients with severe barbiturate intoxication and in 17 patients with acute hepatic necrosis due to paracetamol overdosage. Drug metabolism was strikingly enhanced after barbiturate over-dosage, and this effect was still present six weeks later. In contrast the antipyrine half life was greatly prolonged in patients with paracetamol-induced acute hepatic necrosis but returned to normal or near-normal values within seven to 21 days.

A simple plan for the management of drug overdosage

Using a purely supportive regime of management a survival rate of 99·6 per cent has been obtained in 1,166 patients admitted to hospital as a result of drug overdosage. Based on this experience, the principles of treatment are discussed.

Paracetamol overdose: a plan of management

Four cases of paracetamol overdose are described.

The rationale for the use of dimercaprol, a sulphydryl-containing compound, as a specific antidote is discussed with reference to the pharmacodynamics of paracetamol. A recommended plan of management is presented.

Polymer coating of activated charcoal and its effects on biocompatibility and paracetamol binding

1. The ability of activated charcoal, treated in differing ways with poly(hydroxyethylmethacrylate), to adsorb paracetamol was studied.

2. Activated charcoal was coated with 2, 4 or 10% by weight of poly(hydroxyethylmethacrylate). Neither the percentage by weight (2, 4 or 10%) coating of activated charcoal by the polymer nor the procedure used to apply the coat affected the total adsorption of paracetamol at equilibrium, but these factors did influence the speed of adsorption.

3. The impregnated charcoals, and those with the lowest percentage by weight coating (2%), removed paracetamol from a stirred solution most rapidly. These charcoals also removed the drug most efficiently during column perfusion.

4. Biocompatibility studied in vivo in the dog revealed a smaller fall in blood platelets with haemoperfusion through 4% encapsulated charcoal than with 4% impregnated charcoal.

5. Dye-adsorption studies indicated that impregnation produced less complete coating of the charcoal, and that the lower percentage by weight coatings were the least complete.

6. The most acceptable compromise for clinical use appeared to be the 4% encapsulated charcoal, as the removal of paracetamol was reasonably rapid and the fall in blood platelet levels was acceptable.

Dopamine and serotonin metabolism in hepatic encephalopathy

Patients with stupor or coma from fulminant hepatic failure were found to have high cerebrospinal fluid concentrations of homovanillic acid (HVA) and 5-hydroxyindole acetic acid (5-HIAA), metabolites of dopamine and serotonin respectively. Excessive amounts of their precursors-phenylalanine and tyrosine and free tryptophan-were found in the patients' plasma. Methionine, which participates in dopamine degradation, was also much increased. Similar disturbances were found in patients suffering an acute exacerbation of chronic encephalopathy. These abnormalities would be consistent with other evidence of an increased turnover of serotonin and possibly dopamine in the brain during hepatic encephalopathy.

The binding of paracetamol to plasma proteins of man and pig

The binding of N-acetyl-4-aminophenol (paracetamol) to human and porcine plasma at both toxic and therapeutic concentrations was investigated by ultrafiltration and equilibrium dialysis over the range 50–300 μg ml−1. Plasma protein binding occurred at paracetamol concentrations greater than 60 μg ml−1. The extent of protein binding at a plasma concentration of 280 μg ml−1 of the drug is between 15 and 21% for both pig and man. There is no appreciable binding to erythrocytes in either species over the whole concentration range studied.