To examine if a correlation exists between cytochrome P-450 enzyme induction and disease activity in patients with rheumatoid arthritis (RA), measuring urinary excretion of D-glucaric acid (GA) as an index of phase II drug metabolism.
Patients with RA were treated with sulphasalazine, sodium aurothiomalate, or D-penicillamine in standard dose regimens, for 24 weeks. Patients with ankylosing spondylitis (AS) or non-inflammatory arthritis (NIA) acted as controls. The urinary GA:creatinine ratio was measured at 0, 12, and 24 weeks of treatment.
Patients with RA had a slightly greater urinary GA:creatinine ratio than patients with AS or NIA at baseline; this increased during treatment with disease modifying antirheumatic drugs (DMARDs). Sulphasalazine treatment had a greater effect on GA excretion than sodium aurothiomalate or D-penicillamine; this difference was statistically significant between weeks 0 and 12 (p = 0.01). Gamma glutamyltranspeptidase concentration showed a weak correlation with GA excretion between weeks 0 and 12 (p = 0.03), but all other measurements of changes in disease activity (plasma viscosity, C reactive protein, platelets, and articular index) were found not to correlate with GA excretion between weeks 0-12 or 0-24.
The increased excretion of GA in patients with RA receiving DMARD treatment is probably the result of an indirect effect on hepatic metabolism bearing no relationship to disease activity.