Phenytoin in rheumatoid arthritis.

In a prospective open study, 18 patients with active rheumatoid arthritis were treated with phenytoin (300 mg/day) for 32 weeks. Clinical assessments improved significantly and there was no relapse 8 weeks after drug withdrawal. Serum C-reactive protein, plasma viscosity and hemoglobin also improved but changes were not significant. Serum phenytoin concentrations were lower than anticipated. Side effects were mild and caused 2 patients to withdraw. Our observations and the known effects of phenytoin on the immune system and collagen metabolism suggest that further controlled studies using higher doses are warranted.