Fibrinolysis is the process that leads to the breakdown of blood clots by the action of the serine protease plasmin. Aprotinin is a competitive inhibitor of several serine proteases including plasmin (Sperzel & Huetter 2007). It is a monomeric polypeptide derived from bovine lung tissue. By inhibiting the formation of plasmin and thereby inhibiting fibrinolysis, aprotinin can be used to reduce bleeding during complex surgery (Mahdy & Webster 2004).

Aprotinin has been shown to display anti-SARS-CoV-2 activity against four viral isolates (Bojkova et al. 2020). Protease inhibitors such as aprotinin may prevent virus entry into host cells by preventing the cleavage of the spike protein by ceulluar proteases.