The World Health Organisation Patient Safety Challenge: Medication Without Harm has brought our attention to the importance of medication-related harm as a global public health issue. One of the major contributing factors is polypharmacy, the usage of multiple medicines at the same time. People are getting older and living longer with chronic diseases; they need more medications, which frequently leads to polypharmacy. Subsequently, they are at more risk of medication-related harm. The planned project is an epidemiological study on polypharmacy, medication appropriateness, risk factors, and clinical outcomes post-discharge from a hospital for surgical patients.

The study group hypothesise that pre-and post-operative polypharmacy and potentially inappropriate prescribing is common, especially among older patients, patients with a high comorbidity and frailty burden, and patients undergoing more complicated surgery. Our hypothesis is additionally that preoperative polypharmacy and potentially inappropriate prescribing is associated with a higher short- and long-term mortality, a longer primary hospitalization length of stay, and a higher risk of readmission.

This is an observational, retrospective, single centered study, using clinical data from the patient's medical record from the hospital, the national prescription database of the Directorate of Health, and the and ICD-10 codes from primary care records. For this analysis, medicines will be classified into drug classes based on the first five characters of their WHO Anatomical Therapeutic Chemical (ATC) code. The prevalence (pre) and incidence (post) of polypharmacy (≥5 or more regular medicines) and hyper-polypharmacy (≥10 regular medicines) will be calculated. Potentially inappropriate prescribing will be assessed in individuals ≥65 years applying Beers 2019, Start and Stopp 2014, explicit prescribing criteria. The analysis will be restricted to older individuals, as Beers criteria have not been validated in younger age groups. The anticholinergic burden will be assessed for all individuals ≥18 years will be assessed by applying the anticholinergic burden scale This stratification is important in order to deliver targeted interventions in resource-limited healthcare settings

Inclusion Criteria:

• Participants: surgery patients ≥18 years in admitted to Landspitali University Hospital over the period 2010-2018.

Exclusion Criteria:

• Under 18 years of age

The study population is surgical patients in hospital settings. The cohort will include 100% of tertiary care surgical admissions in Iceland and 70-80% of secondary care in Iceland. The study population includes 56.000 number of participants.