* patients who has partial oxygen saturation below 93% and require immediate hospitalisation after diagnosis * patients, upon initial examination, decided to be hospitalised at the intensive care-unit * inability or unwillingness to give written informed consent * at physicians decision, the trial involvement will not be in patients' best interest, or any condition that does not allow the protocol to be followed safely * patients considered as inappropriate for this study for any reason * active participation in another clinical study * uncontrolled type 1 or type 2 diabetes * severe liver disease (e.g. child pugh score ≥ c, ast\>5 times upper limit) * patients with known severe renal impairment (estimated glomerular filtration rate ≤30 ml/min/1.73 m2) or receiving continuous renal replacement therapy, hemodialysis, peritoneal dialysis * significant cardiovascular co-morbidity (i.e. heart failure) * patients with phenylketonuria (contraindicated for nac) * known allergy for substances used in the study * pregnant or breastfeeding patients, or patients with positive pregnancy test in a pre-dose examination * receipt of any experimental treatment for covid-19 within the 30 days prior to the time of the screening evaluation.

* patients who has partial oxygen saturation below 93% and require immediate hospitalisation after diagnosis * patients, upon initial examination, decided to be hospitalised at the intensive care-unit * inability or unwillingness to give written informed consent * at physicians decision, the trial involvement will not be in patients' best interest, or any condition that does not allow the protocol to be followed safely * patients considered as inappropriate for this study for any reason * active participation in another clinical study * uncontrolled type 1 or type 2 diabetes * severe liver disease (e.g. child pugh score ≥ c, ast\>5 times upper limit) * patients with known severe renal impairment (estimated glomerular filtration rate ≤30 ml/min/1.73 m2) or receiving continuous renal replacement therapy, hemodialysis, peritoneal dialysis * significant cardiovascular co-morbidity (i.e. heart failure) * patients with phenylketonuria (contraindicated for nac) * known allergy for substances used in the study * pregnant or breastfeeding patients, or patients with positive pregnancy test in a pre-dose examination * receipt of any experimental treatment for covid-19 within the 30 days prior to the time of the screening evaluation.

- patients who has partial oxygen saturation below 93% and require immediate hospitalisation after diagnosis - patients, upon initial examination, decided to be hospitalised at the intensive care-unit - inability or unwillingness to give written informed consent - at physicians decision, the trial involvement will not be in patients' best interest, or any condition that does not allow the protocol to be followed safely - patients considered as inappropriate for this study for any reason - active participation in another clinical study - uncontrolled type 1 or type 2 diabetes - severe liver disease (e.g. child pugh score ≥ c, ast>5 times upper limit) - patients with known severe renal impairment (estimated glomerular filtration rate ≤30 ml/min/1.73 m2) or receiving continuous renal replacement therapy, hemodialysis, peritoneal dialysis - significant cardiovascular co-morbidity (i.e. heart failure) - patients with phenylketonuria (contraindicated for nac) - known allergy for substances used in the study - pregnant or breastfeeding patients, or patients with positive pregnancy test in a pre-dose examination - receipt of any experimental treatment for covid-19 within the 30 days prior to the time of the screening evaluation.

- patients who has partial oxygen saturation below 93% and require immediate hospitalisation after diagnosis - patients, upon initial examination, decided to be hospitalised at the intensive care-unit - inability or unwillingness to give written informed consent - at physicians decision, the trial involvement will not be in patients' best interest, or any condition that does not allow the protocol to be followed safely - patients considered as inappropriate for this study for any reason - active participation in another clinical study - uncontrolled type 1 or type 2 diabetes - severe liver disease (e.g. child pugh score ≥ c, ast>5 times upper limit) - patients with known severe renal impairment (estimated glomerular filtration rate ≤30 ml/min/1.73 m2) or receiving continuous renal replacement therapy, hemodialysis, peritoneal dialysis - significant cardiovascular co-morbidity (i.e. heart failure) - patients with phenylketonuria (contraindicated for nac) - known allergy for substances used in the study - pregnant or breastfeeding patients, or patients with positive pregnancy test in a pre-dose examination - receipt of any experimental treatment for covid-19 within the 30 days prior to the time of the screening evaluation.