Leflunomide use in New Zealand. A national prospective post-marketing study

This post-marketing study aimed to record rates of retention, adverse effects and efficacy of leflunomide in the treatment of rheumatoid arthritis (RA). The secondary objectives were to make a semi-quantitative assessment of response to treatment and to examine the effect of a loading dose on adverse events and treatment duration. Rheumatologists in New Zealand contributed to a prospective leflunomide treatment registry. Baseline data were collected on leflunomide initiation and information about treatment experience was sought every 6 months. Each patient was followed for 2 years. Kaplan-Meier analysis was used to evaluate differences in stopping rates between lack of efficacy and adverse effects. Hazard analysis was used to evaluate the effect of using a loading dose on retention rate. Three hundred and eight patients were enrolled in the study; complete follow-up data were available for 244 patients. Retention of patients on leflunomide was 64% at 12 months and 49.4% at 2 years. Reasons for stopping were adverse events (54 patients), loss of effect (25 patients) and miscellaneous reasons (14 patients). Use of a loading dose had no effect on retention; there was no difference in treatment duration between those who stopped from adverse effects or loss of efficacy. Leflunomide was effective in treating RA in a group that had longer duration of disease and greater prior use of disease-modifying agents than the groups studied in clinical trials. Rates of withdrawal were lower than those reported in other post-marketing studies, but were higher than those from phase III clinical trials.