Randomised, double blind, placebo controlled study of interferon β-1a in relapsing-remitting multiple sclerosis analysed by area under disability/time curves

Objectives-The commonly employed outcome measures on disability and relapse rates in treatment trials of relapsing-remitting multiple sclerosis have well demonstrated sensitivity to treatment effects, but their clinical interpretation is problematic. An alternative method of analysis, which is more clinically meaningful and statistically appropriate to a condition with a fluctuating disease course, uses the summary measure statistic "area under the disability/time curve (AUC)", to estimate each patient's total in trial morbidity experience. Methods-The AUC technique was applied in an intention to treat analysis of serial disability data derived from the expanded disability status scale (EDSS), the Scripps neurologic rating scale (SNRS), and the ambulation index (AI), collected during a double blind, randomised, placebo controlled, phase III trial of subcutaneous interferon beta-1a (INF beta-1a) in relapsing-remitting multiple sclerosis (PRISMS Study). The results were compared with the often quoted "conventional" end point of mean change in rating scores from baseline to trial completion. Analyses were also carried out on subgroups with entry EDSS stratified above and below 3.5. Results-EDSS data analysed by AUC normalised to baseline scores disclosed that both doses of IFN beta-1a (22 or 44 mu g) were superior to placebo (p= 0.008 and 0.013, respectively), In addition, the high dose (44 mu g) was more beneficial than placebo using SNRS (p= 0.038) and AI data (p= 0.039). AUC analysis of SNRS scores also showed that for patients with baseline EDSS>3.5, the 44 mu g (but not the 22 mu g) dose was more advantageous than placebo (p= 0.028). Conclusions-Summary measure analysis using the AUC of serial disability/time plots, confirms and extends the results of conventional end point analysis of disability from the PRISMS Study data. AUC evaluations show that high dose INF beta-1a (44 mu g three times weekly) was beneficial on all of the clinical rating scale scores used in this study. This method provides a statistically powerful and clinically meaningful assessment of treatment effects on in trial disability in patients with multiple sclerosis with fluctuating and highly heterogeneous disease courses.