Merit of using risk reduction rather than absolute risk for lipid lowering drugs

EDITOR—Our study of whether treatment recommendations for lipid lowering drugs should be based on absolute coronary risk or risk reduction1 was accompanied by an editorial by Jackson in the same issue that warrants further discussion.

The chance of preventing a coronary event is the absolute risk multiplied by the relative risk reduction, but the question is whether the relative risk reduction is equal in patients of all ages. The meta-analysis of the statin trials by LaRosa et al,2 cited as evidence for this by Jackson (together with three hypertension trials), does not render Law et al's meta-analysis of lipid lowering trials invalid3 as LaRosa et al included both primary and secondary prevention trials, assuming that the difference between them relates only to the absolute risk of a further event.

Our study concerned primary prevention, and the two relevant statin trials in this meta-analysis suggest that age may influence risk reduction, although formal statistical analyses were not reported. One of these trials showed a relative risk reduction of 40% (95% confidence interval 16% to 56%) below the age of 55, compared with 27% (8% to 43%) above4; the other study showed a 46.5% risk reduction below the median age (age 58) compared with 30.4% above.5 Both trials were consistent with the age effect predicted by Law et al's meta-analysis.

Our objective was to highlight the potential for leaving young patients with multiple risk factors untreated by assuming that relative risk reduction is not influenced by age. If treatment is based solely on absolute risk a male, non-smoking, diabetic patient with systolic blood pressure of 180 mm Hg and total and high density lipoprotein cholesterol concentrations of 6.0 and 0.9 mmol/l would not reach the risk threshold for treatment until the age of 53. By contrast, …