Purpose: Alerts for bleeding events are included in the Japanese package inserts of some anti-influenza drugs, including baloxavir marboxil and oseltamivir. However, there are few reports on the incidence of bleeding events during treatment with anti-influenza drugs. This large-scale quantitative assessment compared the incidence of bleeding events in influenza patients treated with baloxavir and other anti-influenza drugs and in untreated patients. Methods: This retrospective cohort study used a large-scale Japanese employment-based health insurance claims database provided by JMDC Inc. and included outpatients diagnosed with influenza between October 1, 2018 and April 11, 2019. Bleeding events were identified by International Classification of Diseases 10th revision codes. Incidences were compared between patients treated with baloxavir or neuraminidase inhibitors and untreated patients. Odds ratios were calculated after exact matching to adjust for potential confounders. Results: Among 529 201 influenza episodes, 30 964 were untreated and 498 237 were treated with anti-influenza drugs: baloxavir, 207 630; oseltamivir, 143 722; zanamivir, 28 208; peramivir, 5304; laninamivir, 113 373. Crude incidence proportions for total bleeding up to 20 days after influenza diagnosis were similar among treated groups, with a slightly higher value for peramivir (0.21% vs. 0.19% for baloxavir, oseltamivir, zanamivir, and laninamivir), and 0.30% in untreated patients. After exact matching, the incidence of bleeding for baloxavir was similar to that for other anti-influenza treatments (odds ratios for baloxavir were 0.90–0.99 compared to other therapies). Conclusions: Based on real-world observation using a large-scale claims database, a similar incidence of bleeding events was observed in recipients of the different anti-influenza drugs.
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