Choudhry NK, Fischer MA, Shrank WH. Influence of Therapeutic Complexity on Medication Adherence in the Netherlands—Reply. Arch Intern Med. 2011;171(9):864-865. doi:10.1001/archinternmed.2011.176
Geers et al applied our measures of therapeutic complexity to statin adherence in the Dutch health care system and found less strong correlations between complexity and adherence than we recently reported.1 Their analysis highlights the importance of context in evaluating research results. Like all studies, our findings are primarily generalizable to settings similar to that of the population evaluated. The US health care system is unique in the extent to which coverage and care are fragmented: patients may receive coverage from private or public sources; drug coverage is often “carved out” and administered separately from medical benefits; patients can receive care from numerous different physicians or other health care providers; and prescriptions may be written by multiple prescribers and filled at many pharmacies on numerous visits. We evaluated this last set of factors and found them to be strongly associated with nonadherence. In contrast, Geers and colleagues' analysis based on a health care system with very little complexity for patients to receive and fill prescriptions found the influence of these factors to be smaller. Rather than contradictory, the results of Geers et al amplify the importance of complexity and the potential role of a “pharmacy home” in the US health care system.
Methodological differences may have also contributed to the apparent discrepancy between analyses. We restricted our measures of complexity because of their overlapping nature (eg, number of fills and long-term medication classes) or collinearity with adherence (eg, patients with more fills are by definition more adherent). Geers et al entered many variables into 1 model; this may have spread the predictive ability among multiple measures of the same construct. We evaluated a linear outcome in contrast to the binary measures used by Geers et al. While these models produce different outputs, the nonsignificant 23% increase in the odds of nonpersistence from poor refill consolidation in the much smaller study by Geers et al generates inferences very similar to those from ours. We assessed complexity during the 90-day period after the first statin fill, whereas Geers et al evaluated complexity during the year prior to the first fill. The burden of medication access and filling may be particularly high after, rather than before, starting therapy, and thus the evaluation by Geers et al may have measured exposure variables that would be expected to have less relationship to adherence.
Notwithstanding these differences, the research letter by Geers et al highlights the difficulties evaluating nonadherence in all health care systems and the need to identify modifiable factors unique to each setting.
Correspondence: Dr Choudhry, Department of Medicine, Brigham and Women's Hospital, 1620 Tremont St, Ste 3030, Boston, MA 02120 (firstname.lastname@example.org).
Financial Disclosure: None reported.
Funding/Support: This work was supported by a research grant from CVS Caremark. Dr Shrank is supported by a career development award from the National Heart, Lung, and Blood Institute (HL-090505).