Abstract
Purpose: Accurate measurement of drug adherence is essential for valid risk-benefit assessments of pharmacologic interventions. To date, measures of drug adherence have almost exclusively been applied for a fixed-time interval and without considering changes over time. However, patients with irregular dosing behaviour commonly have a different prognosis than patients with stable dosing behaviour. Methods: We propose a method, based on the proportion of days covered (PDC) method, to measure time-varying drug adherence and drug dosage using electronic records. We compare a time-fixed PDC method with the time-varying PDC method through detailed examples and through summary statistics of 100 randomly selected patients on statin therapy. Results: We demonstrate that time-varying PDC method better distinguishes an irregularly dosing patient from a stably dosing patient and demonstrate how the time-fixed method can result in a biassed estimate of drug adherence. Furthermore, the time-varying PDC method may be better used to reduce certain types of confounding and misclassification of exposure. Conclusions: The time-varying PDC method may improve longitudinal and time-to-event studies that associate adherence with a clinical outcome or (intervention) studies that seek to describe changes in adherence over time.
Original language | English |
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Pages (from-to) | 325-332 |
Number of pages | 8 |
Journal | Pharmcoepidemiology and Drug Safety |
Volume | 25 |
Issue number | 3 |
DOIs | |
Publication status | Published - 1-Mar-2016 |
Keywords
- Adherence
- Longitudinal
- Methods
- Pharmacoepidemiology
- Time dependence
- controlled clinical trial
- controlled study
- drug dosage form
- exposure
- human
- information processing
- intervention study
- major clinical study
- medication compliance
- randomized controlled trial
- statistics