* current or recent history, as determined by the investigator, of severe, progressive, and/or uncontrolled cardiac disease (nyha class iv), uncontrolled renal disease (egfr \<30 ml/min/1.73 m2), severe liver dysfunction (alt/ast \>5x uln) or bone marrow failure (hb \<80 g/l and anc\<0.5 mm3 and platelet count \<50,000 ul) * women who are pregnant or breastfeeding. * participation in another clinical trial of an investigational medicinal product (ctimp) * known hypersensitivity to the imp or excipients (e.g. lactose) * pre-existing or cconcomittant use of off-label treatments for covid-19 that are not recognised as locally approved standard care. * significant electrolyte disturbance (hyperkalaemia potassium \>5.0 mmol/l or hyponatraemia sodium \< 120mmol/l) * patient currently receiving potassium sparing diuretics that cannot be reasonably withheld * patient currently receiving prophylactic or therapeutic anticoagulantsanticoagulation or antiplatelet agents that cannot be reasonably withheld if randomised to nafamostat * patients (or their partners) planning on donating sperm/eggs during the trial period * ongoing dialysis * history of serious liver disease (child pugh score \> 10) * hemoglobin \< 80 g/l * any known allergy to the imp/excipients * severe uncontrolled diabetes mellitus * in the investigator's opinion, patient is unwilling or unable to comply with drug administration plan, laboratory tests or other study procedures.

* current or recent history, as determined by the investigator, of severe, progressive, and/or uncontrolled cardiac disease (nyha class iv), uncontrolled renal disease (egfr \<30 ml/min/1.73 m2), severe liver dysfunction (alt/ast \>5x uln) or bone marrow failure (hb \<80 g/l and anc\<0.5 mm3 and platelet count \<50,000 ul) * women who are pregnant or breastfeeding. * participation in another clinical trial of an investigational medicinal product (ctimp) * known hypersensitivity to the imp or excipients (e.g. lactose) * pre-existing or cconcomittant use of off-label treatments for covid-19 that are not recognised as locally approved standard care. * significant electrolyte disturbance (hyperkalaemia potassium \>5.0 mmol/l or hyponatraemia sodium \< 120mmol/l) * patient currently receiving potassium sparing diuretics that cannot be reasonably withheld * patient currently receiving prophylactic or therapeutic anticoagulantsanticoagulation or antiplatelet agents that cannot be reasonably withheld if randomised to nafamostat * patients (or their partners) planning on donating sperm/eggs during the trial period * ongoing dialysis * history of serious liver disease (child pugh score \> 10) * hemoglobin \< 80 g/l * any known allergy to the imp/excipients * severe uncontrolled diabetes mellitus * in the investigator's opinion, patient is unwilling or unable to comply with drug administration plan, laboratory tests or other study procedures.

- current or recent history, as determined by the investigator, of severe, progressive, and/or uncontrolled cardiac disease (nyha class iv), uncontrolled renal disease (egfr <30 ml/min/1.73 m2), severe liver dysfunction (alt/ast >5x uln) or bone marrow failure (hb <80 g/l and anc<0.5 mm3 and platelet count <50,000 ul) - women who are pregnant or breastfeeding. - participation in another clinical trial of an investigational medicinal product (ctimp) - known hypersensitivity to the imp or excipients (e.g. lactose) - pre-existing or cconcomittant use of off-label treatments for covid-19 that are not recognised as locally approved standard care. - significant electrolyte disturbance (hyperkalaemia potassium >5.0 mmol/l or hyponatraemia sodium < 120mmol/l) - patient currently receiving potassium sparing diuretics that cannot be reasonably withheld - patient currently receiving prophylactic or therapeutic anticoagulantsanticoagulation or antiplatelet agents that cannot be reasonably withheld if randomised to nafamostat - patients (or their partners) planning on donating sperm/eggs during the trial period - ongoing dialysis - history of serious liver disease (child pugh score > 10) - hemoglobin < 80 g/l - any known allergy to the imp/excipients - severe uncontrolled diabetes mellitus - in the investigator's opinion, patient is unwilling or unable to comply with drug administration plan, laboratory tests or other study procedures.

- current or recent history, as determined by the investigator, of severe, progressive, and/or uncontrolled cardiac disease (nyha class iv), uncontrolled renal disease (egfr <30 ml/min/1.73 m2), severe liver dysfunction (alt/ast >5x uln) or bone marrow failure (hb <80 g/l and anc<0.5 mm3 and platelet count <50,000 ul) - women who are pregnant or breastfeeding. - participation in another clinical trial of an investigational medicinal product (ctimp) - known hypersensitivity to the imp or excipients (e.g. lactose) - pre-existing or cconcomittant use of off-label treatments for covid-19 that are not recognised as locally approved standard care. - significant electrolyte disturbance (hyperkalaemia potassium >5.0 mmol/l or hyponatraemia sodium < 120mmol/l) - patient currently receiving potassium sparing diuretics that cannot be reasonably withheld - patient currently receiving prophylactic or therapeutic anticoagulantsanticoagulation or antiplatelet agents that cannot be reasonably withheld if randomised to nafamostat - patients (or their partners) planning on donating sperm/eggs during the trial period - ongoing dialysis - history of serious liver disease (child pugh score > 10) - hemoglobin < 80 g/l - any known allergy to the imp/excipients - severe uncontrolled diabetes mellitus - in the investigator's opinion, patient is unwilling or unable to comply with drug administration plan, laboratory tests or other study procedures.