(1) Aims of the study: calculating the underreporting ratio for two different medications, a fixed combination of 0.5% timolol + 0.2% brimonidine + 2.0% dorzolamide (antiglaucoma) and a fixed combination of sodium hyaluronate 0.1% + chondroitin sulfate 0.18% (artificial tears) for characterizing the features influencing the reporting of adverse drug reactions (ADRs) in spontaneous reporting. (2) Methods: The underreporting ratio was calculated by comparing the adverse drug reactions reported in the spontaneous reporting database for every 10,000 defined daily doses marketed and the adverse drug reactions from an active surveillance study for every 10,000 defined daily doses used for different drugs (antiglaucoma and artificial tears). The factors related to the report in spontaneous reporting through statistical tests were also determined. (3) Results: The underreporting ratio of spontaneous reporting was 0.006029% for antiglaucoma and 0.003552% for artificial tears. Additionally, statistically significant differences were found for severity, unexpected adverse drug reactions, and incidence of adverse drug reactions in females when compared with spontaneous reporting and active surveillance. (4) Conclusions: The underreporting ratio of ADRs related to ophthalmic medications indicates worry since the cornerstone of pharmacovigilance focuses on spontaneous reporting. Additionally, since underreporting seems to b selective, the role of certain aspects, such as gender, seriousness, severity, and unexpected ADRs, must be considered in future research.
Keywords: active surveillance; adverse drug reaction; antiglaucoma; artificial tears; spontaneous reporting; underreporting.