key: cord-264535-zhz9wzh9
authors: Kow, Chia Siang; Hasan, Syed Shahzad
title: Metformin use amid coronavirus disease 2019 pandemic
date: 2020-06-09
journal: J Med Virol
DOI: 10.1002/jmv.26090
sha: 
doc_id: 264535
cord_uid: zhz9wzh9

There are a few aspects that we would like to add to complement the discussion in EL-Arabey and Abdalla [1]. Firstly, the authors suggested that the reduction of weight with the use of metformin, especially among obese patients, may have a protective effect on mortality from COVID-19. This article is protected by copyright. All rights reserved.

intestinal absorption of vitamin B12 in up to 30% of metformin-treated patients and lowers serum vitamin B12 concentrations by 5% to 10%. 4, 5 The prevalence of vitamin B12 deficiency (or borderline low levels) in metformin-treated patients may approach 20% over 5 years. 5 Since vitamin B12 plays an important role in immune system regulation, its deficiency may negate the potential protective effects, if any, from COVID-19 and its associated mortality. Specifically, cellular immunity, especially related to CD8+cells and the natural killer cells, may be impaired in patients with vitamin B12 deficiency. 6 These cytotoxic lymphocytes (CD8+ T cells and natural killer cells) are important to contain viral infection and they have been observed to decrease significantly during the early stage of COVID-19, which suggests that exhaustion of these cytotoxic lymphocytes facilitates infection from COVID-19. 7 Third, the risk of lactic acidosis from metformin treatment cannot be ignored. Though the incidence of lactic acidosis in metformin users appears to be very low, lactic acidosis related to metformin remains a concern because of the high case-fatality rate. 8 

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