Compliance and adverse event withdrawal: their impact on the west of Scotland Coronary Prevention Study

Aims To assess the additional benefit gained from high compliance in the West of Scotland Coronary Prevention Study and to examine cases where withdrawal from trial medication was due to an adverse event.

Methods The incidence of definite coronary heart disease or non-fatal myocardial infarction, cardiovascular mortality, definite or suspect coronary heart disease death or non-fatal myocardial infarction, the need for coronary revascularization procedures, all-cause mortality and incident cancers were measured in the entire cohort and compared with the high compliance group. The adverse events associated with withdrawal were coded by body system.

Results In subjects with compliance greater than or equal to 75%, treatment with pravastatin resulted in a 38% risk reduction for definite coronary heart disease death or non-fatal myocardial infarction and for cardiovascular mortality, a 46% reduction in risk or coronary revascularization and a 32% risk reduction (P = 0.015) for all-cause mortality.

Conclusions The analysis of the effect of pravastatin in the subgroup of high compliers to randomized medication demonstrated a substantial increase in the estimated risk reductions in comparison with that achieved in the intention-to-treat analysis. This result has significant implications for the motivation of high compliance among patients and for the assessment of the cost-effectiveness of treatment.