Nonadherence with immunosuppressive drugs: U.S. compared with European kidney transplant recipients.

Background: System factors increasingly are suggested as important yet understudied correlates of nonadherence.
Objective: To explore the relationship between healthcare system and prevalence of nonadherence with immunosuppressive regimen by studying variation in nonadherence between European and US kidney transplant recipients and as well as nonadherence in European countries.
Methods: We performed a secondary data analysis on data collected in 3 independent cross-sectional studies using comparable methodology including patients from the United States, the Netherlands, Belgium, and Switzerland. Nonadherence was measured using 1 item of the Siegal questionnaire. Patients were categorized as nonadherent if they reported missing a dose of immunosuppression in the last 4 weeks. Analyses were performed by multiple mixed logistic regression, with center as a random effect and clinical and demographical differences between groups as fixed effects.
Results: 1563 U.S. and 614 European patients from 3 different countries (Belgium [n=187], the Netherlands [n=85], and Switzerland [n=342]) were included. Prevalence of nonadherence in the United States and Europe was 19.3% and 13.2.%, respectively. This higher nonadherence in US patients was confirmed in a multiple logistic regression analysis (OR = 1.78; 95% CI, 1.10-2.89). Nonadherence differed between Belgium (16%) and the Netherlands (14.1%) (OR = 0.27; 95% CI, 0.09-0.80) and between Belgium and Switzerland (11.4%; OR = 0.17; 95% CI, 0.0-0.42).
Conclusion: This is the first study showing differences in prevalence of nonadherence between European and US patients and among European patients. Further research should aim at unraveling the dynamics explaining these differences.