Proton pump inhibitor use and risk of pneumonia: a self-controlled case series study

BACKGROUND: Recent research indicates that use of proton pump inhibitors (PPIs) is associated with pneumonia, but existing evidence is inconclusive because of methodological issues. This study aimed to answer whether PPI-use increases risk of pneumonia while taking the methodological concerns of previous research into account. METHODS: This population-based and nationwide Swedish study conducted in 2005–2019 used a self-controlled case series design. Data came from national registries for medications, diagnoses, and mortality. Conditional fixed-effect Poisson regression provided incidence rate ratios (IRR) with 95% confidence intervals (CI) for pneumonia comparing PPI-exposed periods with unexposed periods in the same individuals, thus controlling for confounding. Analyses were stratified by PPI-treatment duration, sex, age, and smoking-related diseases. Use of histamine type-2 receptor antagonists (used for the same indications as PPIs) and risk of pneumonia was analysed for assessing the validity and specificity of the results for PPI-therapy and pneumonia. RESULTS: Among 519,152 patients with at least one pneumonia episode during the study period, 307,709 periods of PPI-treatment occurred. PPI-use was followed by an overall 73% increased risk of pneumonia (IRR 1.73, 95% CI 1.71–1.75). The IRRs were increased across strata of PPI-treatment duration, sex, age, and smoking-related disease status. No such strong association was found between histamine type-2 receptor antagonist use and risk of pneumonia (IRR 1.08, 95% CI 1.02–1.14). CONCLUSIONS: PPI-use seems to be associated with an increased risk of pneumonia. This finding highlights a need for caution in using PPIs in individuals with a history of pneumonia. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00535-023-02007-5.