Hexa-D-arginine is an inhibitor of furin, with Ki values of 106 nM, 580 nM and 13.2 μM for furin, PACE4 and PC1 respectively.   Pseudomonas aeruginosa exotoxin A (PEA) protein requires furin-mediated cleavage for manifestation of toxicity and hexa-d-arginine effectively blocks PEA-induced cell lysis and is itself noncytotoxic.  Administration of hexa-d-arginine to PEA-treated mice significantly improves their survival rate and decreases circulating levels of tumour necrosis factor alpha.  Hexa-D-arginine also blocks furin mediated SARS-CoV-2 spike protein cleavage to suppress virus production and cytopathic effects.