Statin adherence in coronary outpatients: a novel direct method compared with pharmacy registry data

Abstract Introduction An optimal method to assess adherence to statin therapy is needed. We have developed a novel test analysing atorvastatin, simvastatin and their metabolites in blood, to identify reduced adherence (≥2 consecutively omitted doses). The association between statin adherence measured in blood and long-term adherence is yet to be defined. Purpose To compare statin adherence measured by a single blood test with pharmacy registry data. Methods In a cross-sectional study including 451 patients using either atorvastatin or simvastatin, a spot blood sample was collected 2-35 (median 18) months after a coronary heart disease event. Participants were unaware of the forthcoming statin analyses. Reduced adherence to atorvastatin and simvastatin was determined by drug concentration measurements using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Study data was linked to the pharmacy registry. Indirect adherence was defined by a statin treatment gap exceeding 90 days; i. the three months period prior to the blood test, and ii. from six months before until six months after the blood test. We accounted for overlapping prescriptions of statins. Results Mean age was 61 (SD 9) years, and 19% were women. Thirty-nine (9%) out of 412 patients had reduced adherence to statins, determined by the direct method. The non-adherent patients had higher LDL-cholesterol levels, higher rates of multiple coronary events, lower participation rates at cardiac rehabilitation, and were more often smokers compared with the adherent patients (Table 1). Among patients classified as adherent by the blood test, only one (0.2%) had a treatment gap exceeding 90 days during the preceding three months (Table 2). Correspondingly, of 39 patients with reduced adherence by the blood test, 11 (28%) had treatment gaps exceeding 90 days. The negative agreement between the methods was 97% and the positive agreement 43%. Among patients classified as adherent by the blood test, 21 (5%) had treatment gaps exceeding 90 days from six months before until six months after the blood test. Correspondingly, of 39 patients with reduced adherence by the blood test, 15 (39%) had at least one treatment gap exceeding 90 days. The negative agreement between measurements was 95% and the positive agreement 40%. Conclusions Of 412 coronary outpatients classified adherent by the statin blood test, registry data only identified one patient (0.2%) with a treatment gap exceeding 90 days. The novel blood test emerges as a promising tool to identify patients adherent to statins, and thus may improve lipid management in clinical practice.