Comparing Adverse Event Rates of Oral Blood Glucose-Lowering Drugs Reported by Patients and Healthcare Providers A Post-Hoc Analysis of Observational Studies Published between 1999 and 2011

Background: Non-serious symptomatic adverse drug events (ADEs) affect the real benefit-risk ratio of a drug. Currently, such ADEs are quantified in different ways, often using reports from a healthcare provider or patients, resulting in large variations in estimated rates. Several studies showed that patients report bothersome or symptomatic ADEs more frequently than providers, but no comparisons to an external reference or gold standard have been made. Objective: We conducted a literature review to assess the agreement and concurrent validity of healthcare provider- and patient-oriented methods for quantifying symptomatic ADEs of oral blood glucose-lowering drugs in patients with type 2 diabetes mellitus. Methods: We systematically searched MEDLINE and EMBASE databases for observational studies reporting on rates of ADEs in patients treated for type 2 diabetes that were published between 1999 and 2011. We included nine observational studies reporting absolute rates of symptomatic ADEs in patients receiving monotherapy. We calculated 95% confidence intervals and assessed agreement between rates observed with different methods. We assessed concurrent validity using the range noted in the Summary of Product Characteristics (SPC) as the gold standard. Results: A comparison of rates reported by patients and providers was only possible using three studies of metformin that assessed mainly gastrointestinal (GI) ADEs. Provider-oriented methods by means of medical record review gave lower rates for abdominal pain (0.6-3.7%), dyspepsia (1.3-2.8%) and constipation (0.6-1.0%) than a patient questionnaire method (8.5%, 11.9% and 20.7%, respectively). For diarrhoea, the patient-reported rate (5.2%) was in agreement with the provider-based rates (1.6-7.6%). The majority of the rates reported by providers and patients were not corresponding with the ranges in the SPC. For GI ADEs the rates were all lower, whereas for lactic acidosis and hypoglycaemia the rates were higher. Conclusion: Although it has repeatedly been proposed that patients' reports on safety should be incorporated with providers' reports, especially for symptomatic ADEs, the number of observational studies using patient-oriented methods for assessing ADEs other than hypoglycaemia are limited. Provider-based measurement tended to underestimate symptomatic ADEs. Patient-oriented methods seemed to give ADE rates that were closer to the rates reported in the SPC.