RESUMEN
OBJECTIVE: To evaluate the incidence of medication errors due to dose omissions and the reasons for non-administration of medications. DESIGN: A cohort study blinded to the nursing staff was conducted for 5 consecutive days to evaluate administration of prescribed medications to selected inpatients. SETTING: A major academic teaching hospital in Brazil. PARTICIPANTS: Dispensed doses to patients in medical and surgical wards. MAIN OUTCOME MEASURES: Doses returned to pharmacy were evaluated to identify the rate of dose omission without a justification for omission. RESULTS: Information was collected from 117 patients in 11 wards and 1119 doses of prescribed medications were monitored. Overall, 238/1119 (21%) dispensed doses were not administered to the patients. Among these 238 doses, 138 (58%) had no justification for not being administered. Failure in the administration of at least 1 dose occurred for 58/117 (49.6%) patients. Surgical wards had significantly more missed doses than that in medical wards (P = 0.048). The daily presence of a pharmacist in the wards was significantly correlated with lower frequency of omission errors (P = 0.019). Nervous system medications were missed more significantly than other medications (P < 0.001). No difference was noted in the omission doses in terms of route of administration. CONCLUSIONS: High incidence of omission errors occurs in our institution. Factors such as the deficit of nursing staff and clinical pharmacists and a weak medication dispensing system, probably contributed to incidence detected. Blinding nursing staff was essential to improve the sensibility of the method for detecting omission errors.