Incidence of adverse drug reactions in a tertiary care university hospital in Sao Paulo, Brazil: one year prospective study

Background: The adverse drug reactions (ADRs) are currently a major cause of morbidity and mortality. It’s has been considerable impact on population health and in the costs to the health care.

Objective: To estimate the incidence of ADRs in hospitalized patients in a tertiary care university hospital and to assess the severity and causality of reported ADRs.

Methods: This was a prospective, observational study, carried out between January and December, 2009. All patients admitted at a university hospital following orthopedic trauma, who had received a prescription of medicines were included in the study. The verification of the ADRs was carried out by: (i) spontaneous reporting from health professionals and (ii) active search in the ward by the clinical pharmacist. The incidence of ADRs was calculated based on the number of patients admitted during the study period and the number of ADRs identified. The WHO definition of an ADR was adopted.  The Naranjo algorithm scale was used for causality assessment. All ADRs were classified according to severity. We also identified the time (in days) since the start of treatment until the onset of ADR (time window).

Results: Of the total of 79 ADRs reported, giving an overall incidence of 1.45%. About one third of the reactions (21,27%) were classified as probable, 67% (52) as possible and 6% (8) as defined. The majority of the reactions (74,94%) was mild, 5% (4) moderate and 1% (1) severe. The time window of ADR was (x + SD) 9.4 + 9.9 days (1-41 days). The drug class most frequently involved was antimicrobial agents (55,63%): teicoplanin (13,16%), clindamycin (11,14%) and ciprofloxacin (7,9%), followed by analgesics (20,23% ): tramadol (11,14%) and dipyrone (7,9%). The dermatological system was the most affected (45,57%): exanthema (33,42%), followed by gastrointestinal tract (13,16%): nausea and vomiting (8,10%) and diarrhea (4,5%).

Conclusions: We estimated the incidence 1.45% of ADRs. The majority of the reactions was classified as possible and mild. The exanthema was the most common ADR and the antimicrobial agents were the most involved. This result demonstrates the importance of drug monitoring to ensure the patient’s safety.