The relation between intermittent dosing and adherence: Preliminary insights

Background: The past few years have seen a rapid increase in the introduction of drugs with intermittent dosing schedules (ie, dosed less than once daily). Many of these agents were developed on the assumption that less-frequent dosing would be more convenient for patients and thus contribute to improved adherence, with the potential for improvements in the effectiveness of pharmacotherapy and a reduction in the costs of non-adherence. However, the effect on adherence of intermittent dosing regimens has riot been studied. Objective: This study investigated the evidence to date concerning the effect on adherence of intermittently dosed agents. Methods: Articles from peer-reviewed journals were identified through a search of MEDLINE and International Pharmaceutical Abstracts from 2000 to 2005. The search terms included combinations of intermittent dosing, adherence, compliance, dosing schedule, and dosing regimen. The search focused on articles that reported head-to-head comparisons of older agents having more frequent dosing schedules with newer intermittently dosed agents. Results: Few head-to-head trials were identified that met the inclusion criteria, as most comparative trials of intermittent and daily agents focused on efficacy rather than adherence. Thus, studies of patient preference for the 2 types of agents were included, as preference may have implications for adherence. Eleven trials met the expanded criteria. Overall, adherence was greater with intermittently dosed agents than with more frequently dosed agents for the same conditions; adherence was 8.8% to 12.0% higher for weekly agents than for agents that were dosed once daily. In the single trial of a once-monthly agent, adherence was similar to that with the daily agent over I year (87.4% and 86.6%, respectively). In the studies of patient preference, 61 % to 96% of patients preferred the intermittently dosed agent. Conclusions: In this preliminary review of the available data, once-weekly dosing was associated with improved patient adherence to therapy compared with once-daily dosing. In the only study of a once-monthly agent, adherence was similar to that with the once-daily agent.