High-dose Intravenous N-Acetylcysteine in Mechanically Ventilated Patients with COVID-19 Pneumonia: A Propensity-Score Matched Cohort Study

Background: Current therapies for severe COVID-19, such as steroids and immunomodulators are associated with various side effects. N-acetylcysteine (NAC) has emerged as a potential adjunctive therapy with minimal side effects for patients with cytokine storm due to COVID-19. However, evidence supporting high-dose intravenous NAC in severe COVID-19 pneumonia requiring mechanical ventilation is limited. Methods: We conducted a retrospective analysis of consecutive patients aged ≥ 18 who were admitted for acute respiratory failure (PaO2/FiO2 ratio <300) with SARS-CoV-2 infection to the Intensive Care Unit (ICU) of Queen Elizabeth Hospital from fifth July 2020 to 31^st October 2022. Inclusion was limited to patients who required mechanical ventilation. High-dose NAC refers to a dosage of 10 g per day. The primary outcome was all-cause mortality within 28 days. Propensity-score matched analysis using logistic regression was performed. Results: Among the 136 patients analyzed, 42 (40.3%) patients received NAC. The unmatched NAC patients displayed a higher day-28 mortality (12 (28.6%) versus 4 (6.5%), p = 0.005) and fewer ventilator-free days (18.5 (0-23.0) versus 22.0 (18.3-24.0), p = 0.015). No significant differences were observed in ICU and hospital length of stays among survivors. In patients who were not treated with tocilizumab, those receiving NAC exhibited a trend toward a quicker reduction in C-reactive protein compared to those who did not receive NAC.After propensity score matching which included 64 patients with 33 (51.6%) receiving NAC, no significant differences were found in 28-day mortality, ventilator-free days, or ICU and hospital length of stay. After adjusting for potential confounders, logistic regression of the propensity score-matched population did not demonstrate that the use of NAC independently affected 28-day mortality. Conclusions: In patients with COVID-19 pneumonia requiring mechanical ventilation and receiving standard COVID-19 treatment, the addition of high-dose NAC did not lead to improved clinical outcomes.