Prevalence, risk factors and main features of adverse drug reactions leading to hospital admission

Purpose To assess the prevalence of hospital admission related to adverse drug reactions (ADRs) in a third-level hospital, to analyse the associated factors, and to describe the reactions and the drugs involved. Methods A cross-sectional study was conducted for a 120-day period. Patients that were urgently hospitalized entered the study. The primary endpoint was the ADR-related urgent admission. A descriptive analysis of demographic, clinical, and drug-related variables was performed. The association between the likelihood of urgent admission due to ADRs and age, gender, and number of drugs used was analysed. A descriptive analysis of the suspected drugs and the reactions in ADR-related admissions was performed. Results Overall, 186 out of 4,403 hospital admissions were due to ADRs (prevalence: 4.2 % [95 % CI 3.7–4.8 %]). Age (≥65 years: OR 1.59 [95 % CI 1.10–2.29]) and number of drugs used at the time of admission (3–5 drugs: OR 5.07 [95 % CI 2.71–9.59]; 6–9 drugs: OR 5.90 [95 % CI 3.16–11.0]; ≥10 drugs: OR 8.94 [95 % CI 4.73–16.89]), but not gender, were identified as independent factors associated with ADR-related hospitalization. The overall in-hospital stay for patients admitted with ADRs amounted to 1,785 days. The ADRs were mainly type A reactions (92 %). Acute renal failure related to renin-angiotensin system inhibitors, haemorrhage due to anticoagulants, and upper gastrointestinal bleeding related to antiplatelet drugs and/or non-steroidal anti-inflammatory drugs were the most frequent. Conclusion Over 4 % of urgent hospitalizations are caused by ADRs, which are dose-related and predictable in more than 90 % of cases. The main risk factors are advanced age and polypharmacy.