All hospitalized adult patients (defined as 18 years or older at the moment of discharge) discharged from participating hospitals from in 01-07-2012 until 01-07-2013 will be included, if they were treated at any moment during hospitalization with AST (both H2A, defined as all drugs belonging to ATC A02BA, and PPI, defined as all drugs belonging to ATC A02BC). Younger patients are excluded as they are often treated with compounded suspensions and these preparations are impossible to match with the dispensed medication. Fulfillment of these criteria will be based on queries retrieving data from the hospital information system. The query will generate, for each participating hospital, a list of unique hospitalizations. In order to guaranty the patients privacy, datasets will be made anonymous by a trusted third party (see further in protocol). Reporting will be anonymous, never on an individual patient, physician or hospital.