Study aim: 1. To compare serum levels of liver aminotransferases, bilirubin and prothrombin time between Covid-19 patients receiving remdesivir with and without simultaneous acetylcysteine therapy 2. To compare the incidence of acute liver injury between Covid-19 patients receiving remdesivir with and without simultaneous acetylcysteine therapy Design: A double-blind, placebo-controlled randomized clinical trial. Patients will be randomized using QuickCalcs random-number calculators (2018 GraphPad Software, LLC; San Diego, CA). Settings and conduct: Intensive care unit of Imam Reza Hospital (501 Hospital, AJA University of medical Sciences) Participants/Inclusion and exclusion criteria: َAll patients aged above 18 years admitted in intensive care unit with definite diagnosis of Covid-19 under treatment with remdesivir will be included. Criteria of exclusion will be: 1. Positive history of any underlying liver disease 2. Plasma levels of liver transaminases over 100 IU/L on the first day of ICU admission 3. Simultaneous use of any hepatotoxic drugs Intervention groups: One gram acetylcysteine will be administered intravenously every 12 hours for each patient in the intervention group, and each patient in the placebo group will receive the same volume of 0.9% sodium chloride. Main outcome variables: Outcome of interest will be considered as any significant difference in serum levels of aspartate aminotransferase, alanine aminotransferase, bilirubin, prothrombin time or incidence rate of acute liver injury between intervention and placebo groups on the second, third, forth or fifth day of trial.