Lower Proportion of Spontaneous Adverse Event Reports for Generic Drugs by Comparison With Original Branded Drugs at the Postmarket Stage in Japan

We investigated impacts of increased generic drug use on spontaneous adverse event reports (SAERs), because SAERs have been a major source of data for drug safety assessment at the postmarket stage. Reporting proportion of SAERs for the generic drugs was consistently and significantly lower than that for the original branded drugs. The reporting proportion targeting for 55 active product ingredients, which had the longest follow-up period after generic drug marketed, gradually decreased for the original branded drugs and increased for the generic drugs. However, these transitions did not parallel the changes in market share over the same period. These results suggest that the reporting proportion of SAERs for generic drugs may not keep pace with growth in market share. When generic drugs account for the majority of market share, utilization of multiple sources of information and data, in addition to SAERs, may be a key to assuring drug safety at the postmarket stage.