Does a single-pill antihypertensive/lipid-lowering regimen improve adherence in US managed care enrolees? A non-randomized, observational, retrospective study.

BACKGROUND: A previous study in 4703 patients suggested that a single-pill combination of amlodipine and atorvastatin is associated with greater adherence to therapy than a two-pill calcium channel antagonist (calcium channel blocker [CCB]) and HMG-CoA reductase inhibitor (statin) regimen. However, the impact of prior medication use on the potential adherence benefits of single-pill amlodipine/atorvastatin has not been studied.
OBJECTIVE: To compare adherence to single-pill amlodipine/atorvastatin versus two-pill CCB + statin regimens in a large managed care population, stratified according to prior CCB and statin use.
METHODS: This retrospective study was conducted among managed care enrolees in the US. Patients included in the analysis had to have a pharmacy claim for single-pill amlodipine/atorvastatin or claims for both a CCB and a statin within any 30-day window between April 2004 and April 2005. Adherence was measured over 6 months following the index date (the date of the first single-pill amlodipine/atorvastatin claim or of the claim for the second medication class for any two-pill CCB + statin regimen) as the proportion of days covered (PDC) by both CCB and statin therapy; patients were considered 'adherent' if PDC was > or =80%. Patients were divided into four cohorts based on pre-index CCB and statin use: (i) naive (CCB)/naive (statin); (ii) experienced (CCB)/naive (statin); (iii) naive (CCB)/experienced (statin); and (iv) experienced (CCB)/experienced (statin). Within each cohort, adherence was compared for patients receiving single-pill amlodipine/atorvastatin versus two-pill amlodipine + atorvastatin or other two-pill CCB + statin regimens (including amlodipine or atorvastatin but not both) at index. Multivariable logistic regression with propensity score weighting was used to adjust for covariates, including age, sex and co-morbidities.
RESULTS: In total, 35,430 patients were included in the analysis. At month 6 (after adjusting for covariates), patients in the experienced (CCB)/naive (statin) cohort receiving single-pill amlodipine/atorvastatin were more than twice as likely to be adherent as those receiving two-pill amlodipine + atorvastatin (odds ratio [OR] 2.20; p < 0.0001) or other two-pill CCB + statin regimens (OR 2.75; p < 0.0001). Similarly, patients in the naive (CCB)/experienced (statin) cohort receiving single-pill amlodipine/atorvastatin were more likely to be adherent than those receiving two-pill amlodipine + atorvastatin (OR 1.72; p < 0.0001) or other two-pill CCB + statin regimens (OR 2.81; p < 0.0001). In contrast, in the naive (CCB)/naive (statin) cohort there was no significant difference in adherence between patients receiving single-pill amlodipine/atorvastatin versus two-pill amlodipine + atorvastatin (OR 1.00), although patients receiving single-pill amlodipine/atorvastatin were slightly more likely to be adherent than those receiving other two-pill CCB + statin regimens (OR 1.29; p < 0.01). In the experienced (CCB)/experienced (statin) cohort there was also no significant difference between patients receiving single-pill amlodipine/atorvastatin versus two-pill amlodipine + atorvastatin (OR 1.08), and only a slightly greater likelihood of achieving adherence to single-pill amlodipine/atorvastatin versus other two-pill CCB + statin regimens (OR 1.19; p < 0.01).
CONCLUSIONS: This large retrospective study confirms previous observations that single-pill amlodipine/atorvastatin can help improve adherence versus two-pill CCB + statin regimens. However, greater improvements in adherence are likely to be observed in patients with prior experience of either CCB or statin therapy than in those either naive to, or experienced with, both therapies.