(065) A comprehensive overview of dispensing durations for all drugs applicable in pharmacoepidemiological studies using Danish data

Publication Number: 728

Background: Optimal quality of pharmacoepidemiological research relies on correct building of treatment episodes from dispensing data, which in turn depends on the ability to assign treatment duration to a single dispensing. The reverse parametric waiting time distribution (rWTD) is a particularly attractive data-driven method to estimate such dispensing durations.

Objectives: To provide a publicly available resource of estimated dispensing durations for use in applied pharmacoepidemiology.

Methods: We used data from a 20% sample of all Danish residents in 2019 and information on their redemptions of all commonly used drugs. Drugs were identified by their ATC code (7 digits). For each drug we applied the reverse WTD with a random index date to estimate the mean (mu) and variance (sigma) for the distribution of distances (natural logarithmic scale) between dispensings belonging to the same treatment episode (log-Normal interarrival density). We calculated the 90th and the 95th percentiles for the interarrival density. We also obtained estimates stratified on sex and age groups (18-70 and 70+ years). We finally allowed inclusion of volume dispensed as a covariate. A spreadsheet and an online tool was developed to provide access to estimates for all drugs, with and without stratification on sub-groups and with or without adjustment for volume dispensed and allowing for calculation of percentiles by choice.

Results: Dispensing duration percentiles could be estimated for 340 drugs in 2019. The most commonly used drug was Paracetamol (ATC: N02BE01) followed by Ibuprofen (ATC: M01AE01). The estimated 90th percentile for Paracetamol was 148.1 (95% CI: 147.1; 149.1) days ignoring volume dispensed.

Conclusions: We provide a comprehensive overview of dispensing durations for all drugs registered in the Danish National Prescription Registry for use in pharmacoepidemiological research. Data is presented in an online tool and in a downloadable spreadsheet facilitating dissemination and use of results.