Confidence and accuracy in identification of adverse drug reactions reported by outpatients.

Background Patient reporting of adverse drug reactions (ADRs) could supplement the existing reporting system and contribute to early detection of ADRs. The confidence in ADR identification and their attribution of ADRs were limited to outpatients. Objective To determine the type and frequency of ADRs reported by outpatients, to evaluate confidence and accuracy in ADR identification as well as contributing factors. Setting University hospital in northeastern Thailand Method Cross-sectional study using questionnaires distributed to 500 outpatients who claimed to have experienced an ADR. Confidence in identifying ADRs was measured by visual analogue score (VAS), while accuracy of reported ADRs was determined using Naranjo algorithm and WHO criteria. Main outcome measure Number and type of ADRs, confidence rating and accuracy category. Results In total, 390 outpatients completed the questionnaire (response rate = 78.0%). Rash (19.0%), nausea/vomiting (7.4%), and dizziness (5.8%) were the top three reported ADRs. Sixty-one percent of respondents rated their level of confidence in identifying ADRs as high (VAS 9.2 ± 0.95), which was associated with having underlying diseases (OR 1.93), low number of reported symptoms (OR 0.38) and severe ADRs (OR 1.33). Causality assessment was classified as true ADRs in 90.0% and 88.9% of cases, using Naranjo algorithm and WHO criteria, respectively. Respondents with low number of reported symptoms (OR 0.27) and high level of confidence had greater accuracy in ADR identification (OR 1.11). Conclusion The outpatients reported a high proportion of potential ADRs with high confidence and accuracy. Patient reporting of ADRs has potential to support the pharmacovigilance system.