NOTE: THIS VERSION HAS BEEN UPDATED FROM THE PUBLISHED PROCEEDINGS. WE CORRECTED THE FIGURES AND CLARIFIED THAT THE MEDICATION POSSESSION RATIO IS THE DEFAULT MEASURE OF ADHERENCE

The Medication History Estimator (MHE) is designed to output data at the course-level; i.e., one row of data per drug course. Course and period Medication Possession Ratios (MPRs) are calculated for each medication. Reports that describe the frequency and percent of users for each medication product, average duration of medication courses, medication possession ratios, and Kaplan-Meier based persistency curves are automatically generated and formatted for professional reports and journal publications. Estimating each patient's medication exposure is a fundamental component of any study that aims to evaluate the safety or effectiveness of medication therapy in an observational setting. When investigators design studies that evaluate medication exposure or compare medications they are confronted with a series of decisions concerning how to characterize treatment histories and classify treatment groups. Example decisions include whether to conduct an intention-to-treat analysis or to evaluate only outcomes during medication exposure. Researchers must also decide on criteria for identifying incident or new courses of drug therapy rather than utilizing established courses. The approach used to infer a patient's treatment history from medication orders or dispensing data influences cohort identification and treatment group classification. Nevertheless, descriptions of methods are typically not adequately explicit to replicate study procedures directly from the published narrative. This is due to the fact that journals govern the distribution of scientific findings while the task of distributing methods and protocols is customarily relegated to authors.(4) To be compliant with the basic principles of transparency, reproducibility and reusability(2, 4, 7) we developed a generalized approach to estimate medication histories that can be used to summarize medication exposure in a population and to structure data for epidemiological evaluation. The approach is considered "generalized" because the program can be used to estimate medication histories for any drug therapy and it is flexible enough to allow a vast number of unique parameterizations. This paper describes the features of the SAS program and presents example output data structures and reports. The Medication History Estimator (MHE) is designed to output data at the course-level - i.e., one row per drug course. A course and period Medication Possession Ratio (MPR) is calculated for each medication. Reports that describe the frequency and percent of users for each medication product, average duration of medication courses, medication possession ratios, and Kaplan-Meier based persistency curves are automatically generated and formatted for professional reports and journal publications.