Effect of calcium channel blockers on influenza incidence: a population-based retrospective cohort study using administrative claims data in Japan.

Laboratory experiments have indicated that calcium channel blockers (CCBs) inhibit the entry and replication of influenza A virus in cells. However, no clinical studies have assessed the incidence of influenza among patients receiving CCBs. This study aimed to investigate the association between CCB use and the incidence of influenza among patients with hypertension using administrative claims data in Japan. Retrospective cohort study. Administrative health insurance claims database of Kumamoto Prefecture, Japan. 360 515 patients with hypertension (10th edition of the International Classification of Diseases code I10) who were prescribed CCBs and 171 142 patients who were prescribed angiotensin-converting enzyme inhibitors (ACEIs)/angiotensin receptor blockers (ARBs) between 2012 and 2016. We compared the incidence of influenza between the CCB and ACEI/ARB groups using high-dimensional propensity-score (HD-PS) matching. A total of 166 814 HD-PS matched pairs were obtained. Before HD-PS matching, the CCB group had a significantly lower influenza incidence than the ACEI/ARB group in the overall analysis (2.4% vs 2.5%, p=0.007; risk ratio 0.95, 95% CI 0.92 to 0.99). However, no significant difference was observed between the two groups after HD-PS matching (2.4% vs 2.5%, p=0.067; risk ratio 0.96, 95% CI 0.92 to 1.00); only in 2012 did the CCB group have a significantly lower likelihood of influenza than the ACEI/ARB group. No significant difference was observed in the influenza incidence between the CCB and ACEI/ARB groups. A direct comparative study between background-matched patients with and without CCBs is warranted to confirm the effect of CCBs on reducing the incidence of influenza.

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Competing interests: None declared.