Metabolism of low-dose paracetamol in patients with rheumatoid arthritis.

1. Low dose (500 mg) paracetamol (acetaminophen) was administered to patients with rheumatoid arthritis (RA) and to age-matched healthy controls and to hospital controls. 2. At this dose level, patients with RA excreted decreased amounts of paracetamol sulphate (controls means 11.3 +/- 5.1, 10.6 +/- 5.9; RA mean 3.02 +/- 3.7). This difference is statistically significant (P less than 0.001). 3. The mean ratio of excretion of paracetamol sulphate/paracetamol glucuronide was 5.6 +/- 12.1, 5.3 +/- 10.7 in controls but 2.1 +/- 2.7 in RA patients (P less than 0.001). 4. Patients with RA appear to have less capacity for excreting paracetamol as non-toxic conjugates and may be more susceptible to paracetamol toxicity, especially on chronic dosage.