Based on this dataset an estimate on cost of AST from a healthcare payer perspective will be calculated using the list price (= public price) at 01-07-2013 of the involved medication. In combination with the results of ASTRA-2 the impact of parameters like percent of appropriateness, duration of therapy, diagnosis and comorbidities will be studied in a multivariate analysis. As the main dataset from ASTRA-2 comes from UZ Leuven, the other participating hospitals are each requested to review 20 medical files from their hospital in order to investigate possible extrapolation bias or to support the findings.