BACKGROUND: Information required to calculate the dispensed numberof days of treatment (NoDT) of individual prescriptions or dispensingis often incompletely recorded and may vary substantially across dif-ferent sources of routinely collected electronic health data (EHD). Asa result, different assumptions on treatment dose and duration mightbe necessary according to the information that is available. This raisesconcerns over heterogeneity in the way that exposure is defined andreported, as well as how to interpret the results of studies using multi-ple EHD sources.
OBJECTIVES: To i) standardize the terms and variables needed whencalculating NoDT across different EHD, and ii) define a series ofassumptions and calculation options that can be adapted to differentEHD depending on the availability of prescription, dispensing, admin-istrative, and product information.
METHODS: We compiled a list of common information on medicinalproducts that may be captured (or not) in EHD. Guidelines ofEuropean standard terms for medicines were reviewed and a“cook-book”of unique algorithms to calculate NoDT, i.e. recipes, wasderived.
RESULTS: Variables describing medicinal products used to estimateNoDT were established and terms harmonized, such as the amount ofactive principle per day, basic dose forms to be administered to thepatient, or options for administration routes. Four main recipes with our variants were created for NoDT calculation on the basis of thevariables. For example, through the number of forms per box and theprescribed forms per day as denominator (num_forms_per_box)/(pre-sc_forms_per_day); or, instead of using forms, amounts(e.g. (dosage_amount_per_box)/(presc_amount_per_day)). In the casethat only the product name is known, the amount of medicinal prod-uct in the box should be extracted from the product name and dura-tion estimated through prescribed or defined daily doses. Modelexamples of how these calculations can be made with different typesof medicinal products (tablets, combinations, syrup, topicals, vials,inhalations, powder, etc) were created.
CONCLUSIONS: There is heterogeneity in the information required toestimate NoDT, which may lead to heterogeneity in the definition ofexposure when cross-national studies are performed. We provide ter-minology and rules to harmonize available information to calculateNoDT, to enhance the comparability of exposure definitions acrossdata sources.
