Population pharmacodynamics of romazarit

1. The response to romazarit, a disease modifying anti-rheumatoid agent, was observed in patients with rheumatoid arthritis (RA) in a double-blind placebo controlled study. 2. Two hundred and twenty-four patients were recruited from 11 centres and treated with placebo or romazarit at a dose of 200 mg or 450 mg every 12 h for up to 24 weeks. Disease activity was measured using the Ritchie Index (RI). Plasma concentrations of romazarit were measured at each of up to eight assessments of RI. 3. The effect of romazarit was examined using analysis of variance (ANOVA) in 164 patients who contributed 61% of observations of disease activity. Observations after 12 weeks of treatment were excluded from ANOVA. 4. A population pharmacokinetic-dynamic model for the time course of disease progress and the response to placebo and romazarit was used to describe observations from all patients. 5. The population model suggested that the effect of romazarit was on the rate of progress of the disease and was describable by an Emax model. Concentration was a better predictor of response than dose. 6. Romazarit was significantly better than placebo in improving the RI in patients with RA. The placebo efficacy of romazarit treatment was similar to that associated with placebo treatment. 7. The population model provided a more complete description and explanation of the clinical pharmacology and therapeutic potential of romazarit than ANOVA.