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Statin adherence and outcomes

Study
Results
Comment

Taking effective medicines is likely to produce better results than keeping them in the cupboard. An observational study might be expected to find that result. A potential problem with the simplistic interpretation might be that patients who are most concordant are different in some way from those who are least - what is known as the healthy adherer effect. A new study looks at this and indicates that benefits of statins are related to adherence alone [1].

Study

The study was a longitudinal observational study of 31,500 patients aged at least 66 years who survived a myocardial infarct between 1999 and 2003 in Ontario, and who filled at least one prescription for statin, beta-blocker, or calcium antagonist within three months. For inclusion, at least 15 months of follow up information had to be available.

Computerised prescription records allowed the proportion of days covered by each therapy to be calculated. High, intermediate, and low adherence were defined as ≥80%, 40-79%, and ≤40% of days covered by therapy. The outcome was mortality overall, stratified by adherence and initial disease severity (high, intermediary, and low mortality risk according to age, sex, and severity of cardiac disease).

Results

Statins were used at least once by 17,800 patients, with 24,300 using a beta-blocker and 9,200 a calcium antagonist. One year average adherence rates were 88%, 84%, and 79% respectively. The proportion of patients stopping their drugs entirely during the overall 2.4 years of follow up was very low, 1.1% for statins, 1.7% for beta-blockers, and 3.2% for calcium channel blockers. For all three drug classes, most patients had high adherence ≥80% (68% to 81%).

For statins, compared with high adherers, the risk of mortality was 12% higher with intermediate adherence and 25% higher with low adherence. The effects with different rates of adherence and initial mortality risk are shown in Figure 1. There was a small, just significant trend to higher mortality with lower adherence for beta-blockers, and no difference with calcium channel blockers.



Figure 1: Mortality in high, intermediate, and low risk with different levels of adherence to statins





Comment

Calcium channel blockers have no proven survival advantage after myocardial infarction, and there was no difference in mortality between high and low adherers. This forms a control to demonstrate that there was no special effect of high adherence per se, and that the effects seen with statins and beta-blockers, and especially with statins, were due to the drug classes used. So we can confidently say that, in this case, common sense rules. Keep taking the statins is the order of the day.

Reference:

  1. JN Rasmussen et al. Relationship between adherence to evidence-based pharmacotherapy and long-term mortality after acute myocardial infarction. JAMA 2007 297: 177-186.

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