Nafamostat and camostat are serine protease inhibitors both approved in Japan for use against pancreatitis in humans. Camostat was previously found in vitro to block the entry of SARS-CoV by acting as an antagonist to the serine protease TMPRSS2, and researchers believe both nafamostat and camostat could have a similar effect in inhibiting SARS-CoV-2. In vitro, both have been found to block the entry of SARS-CoV-2 into cells, although one preprint study reported that nafamostat inhibited viral cell entry with an efficiency roughly 15-fold higher than that of camostat.

These drugs are undergoing phase 2 and phase 2/3 clinical trials in the USA and Japan for their effectiveness against COVID-19, the primary outcome of which will be time to clinical improvement for nafamostat and reduced viral load after treatment for camostat.

“These drugs are quite old, they’re well studied, they have known targets that are exactly the same protease that the virus uses,” says Anton Yuryev, professional services director at Elsevier, who has done screenings for possible COVID-19 drug treatments.