This study aims to synthesize evidence on dipeptidyl peptidase-4 (DPP-4) inhibitor and mortality in COVID-19 patients and factors affecting it.
We performed a systematic literature search from PubMed, Scopus, and Embase databases from inception of databases up until 7 March 2021. Studies that met all of the following criteria were included: 1) observational studies or randomized controlled trials that report COVID-19 patients, 2) reporting DPP-4 inhibitor use, 3) mortality, and 4) mortality based on DPP-4 inhibitor use. The exposure was DPP-4 inhibitor, defined as DPP-4 inhibitor use that started prior to COVID-19 hospitalization. The control group was patients with no exposure to DPP-4 inhibitor. The outcome was mortality. The pooled effect estimate was reported as risk ratio (RR).
There were 4,477 patients from 9 studies in this systematic review and meta-analysis. 31% of (15%, 46%) the patients use DPP-4 inhibitor. Mortality occurs in 23% (15%, 31%) of the patients. DPP-4 inhibitor was associated with lower mortality in patients with COVID-19 (RR 0.76 [0.60, 0.97], p = 0.030, I2: 44.5%, p = 0.072). Meta-regression analysis showed that the association between DPP-4 inhibitor and mortality was significantly affected by metformin (RR 1.02 [1.00, 1.04], p = 0.048) and angiotensin converting enzyme inhibitor or angiotensin receptor blocker (ACEI/ARB) use (RR 1.04 [1.01, 1.07], p = 0.006), but not age (p = 0.759), sex (reference: male, p = 0.148), and hypertension (p = 0.218).
DPP-4 inhibitor use was associated with lower mortality in COVID-19 patients, and the association was weaker in patients who were also taking metformin and/or ACE inhibitors.

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