A Catalogue of Dispensation Lengths for Building Treatment Episodes—Application of the Waiting Time Distribution to All Commonly Prescribed Drugs in Denmark

BACKGROUND: In pharmacoepidemiologic research, correct assignment of the length of single dispensation is critical to build treatment episodes. The parametric reverse waiting time distribution (rWTD) is a particularly attractive data-driven method to estimate dispensation lengths. AIM: To provide an easily accessible resource of estimated dispensation lengths covering all commonly used drugs for use in treatment episode building in applied pharmacoepidemiologic research. METHODS: We used a random 20% sample of the Danish population alive after 1st January 2000 and identified all their prescriptions filled between 2010 and 2022. We applied the rWTD with five random index dates for each individual to estimate parameters that allow calculation of dispensation length estimates. Parameters were estimated with and without age, sex, and dispensed amount as covariates. RESULTS: We present estimated dispensation lengths for the 20 most prescribed drugs and drug classes in Denmark. Estimated dispensation lengths for all drugs are provided online, and in a spreadsheet. The most prescribed drug was paracetamol with an estimated dispensation length of 194 days, while atorvastatin was the most commonly used drug indicated for long-term use with an estimated dispensation length of 165 days. The dispensation lengths for drugs varied according to age, dispensed volume, sex, and over time. CONCLUSIONS: This is a comprehensive overview of dispensation lengths for all commonly prescribed drugs registered in the Danish National Prescription Registry. Data presented in an online resource can be utilized and modified by other researchers providing optimal conditions for high quality pharmacoepidemiologic research.