Effective prevention of cardiovascular disease and diabetes‐related events with atorvastatin in Japanese elderly patients with type 2 diabetes mellitus: Adjusting for treatment changes using a marginal structural proportional hazards model and a rank‐preserving structural failure time model

Abstract

To assess the preventive effect of atorvastatin on cardiovascular disease and on diabetes-related events in elderly type 2 diabetic patients enrolled in the Japanese Elderly Diabetes Intervention Trial (J-EDIT). Data were obtained from 1173 patients aged 65-84 years who were enrolled in the J-EDIT. Patients were followed prospectively for 6 years to determine the effects of atorvastatin on serum cholesterol levels, and cardiovascular and diabetes-related events. Because the study protocol allowed atorvastatin to be prescribed according to the clinical needs of each patient, we regarded the J-EDIT data as if they came from a cohort study. We adjusted for clinical characteristics during the study as time-dependent confounders using two methods, inverse-probability-of-treatment (IPT) weighting and g-estimation method. The total follow-up period was 5310.8 person-years (5.7 years of median follow up), during which 202 patients received atorvastatin treatment. Atorvastatin was associated with moderate reductions in cholesterol levels: 24.2 mg/dL for total cholesterol, 22.9 mg/dL for low-density lipoprotein (LDL) cholesterol and 24.3 mg/dL for non-high-density lipoprotein cholesterol at the first post-treatment year. As a result, the proportion of patients who achieved targeted levels of LDL cholesterol clearly increased after atorvastatin treatment. Eight patients in 476.6 person-years among atorvastatin-treated and 113 untreated patients in 4721.4 person-years had cardiovascular events (the composite end-point of fatal/non-fatal myocardial infarction, angina pectoris, coronary intervention, and fatal/non-fatal cerebrovascular disease); hazard ratio (HR) = 0.48, 95% confidence interval (CI) = 0.19-1.16, P = 0.10, and HR = 0.32, 95% CI = 0.05-1.87, P = 0.21 from IPT weighting and g-estimation method, respectively. Furthermore, seven in 475.0 person-years among atorvastatin-treated and 149 untreated patients in 4682.4 person-years had diabetes-related events (the composite end-point of sudden death, renal failure death, death as a result of hyperglycemia or hypoglycemia, diabetic gangrene and congestive heart failure in addition to cardiovascular event); HR = 0.30, 95% CI = 0.12-0.77, P = 0.01, and HR = 0.40, 95% CI = 0.09-0.89, P = 0.03 from IPT weighting and g-estimation method, respectively. When cardiovascular events were further differentiated into coronary vascular and cerebrovascular events, atorvastatin especially decreased the cerebrovascular risk. The use of atorvastatin to lower cholesterol levels in elderly Japanese patients with type 2 diabetes mellitus appears to reduce the risk of cardiovascular and diabetes-related events.