**3. Epidemiology of adverse drug reactions**

Adverse drug reactions (ADRs) are considered to be among the leading causes of morbidity and mortality. Around 5-25% of hospitals admissions are estimated to be due to ADRs and about 6-15% of hospitalized patients experience serious ADRs (SADRs) causing significant prolongation of hospital stay and projected that adverse drug events are the fourth to sixth leading cause of death in the United States. Most studies are focused on rates of serious and fatal events in hospitalized patients, probably because tracking of ADRs is more established in the inpatients setting. An English study (Kane-Gill, 2010) found an increase in hospitalizations caused by ADR in about 76.8% in ten years. A recent study of administrative health-care data found an annual ADR prevalence rate of 0.5% among ambulatory-care patients; however, the authors acknowledge this is probably an underestimate of true ADR rates. Ambulatory-care patients experiencing an ADR were younger on average than hospitalized patients.

Risk factors of suffering adverse drug events are: women, elderly and polipharmacy mainly. Women were more likely than men to have ADRs in both outpatients and inpatients settings. In the study from Zopf (2008), the OR of women from suffering ADR was 1.562; (95% CI 0.785, 2.013). Other risk factors implicated in adverse drug reactions are elderly, drug-drug interactions, polipharmacy and renal insufficiency. In the study of Sanchez Muñoz (2011), also drug-drug interactions were as important as age and renal insufficiency in producing adverse drug reactions.

Patients affected by adverse dug events are admitted in internal medicine department and geriatrics quite often, but patients hospitalized in Intensive care units and pediatrics also suffer from these problems.
