Is teicoplanin a complementary treatment option for COVID-19? The question remains

We read with great interest the editorial by Baron et al. suggesting the potential use of teicoplanin as an alternative drug to treat patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [1]. Indeed, this glycopeptide antibiotic, commonly used to treat Gram-positive bacterial infections, also showed potential complementary antiviral activity against severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV) and Ebola virus, as previously highlighted by Zhou et al.; moreover, influenza A and B viruses and feline infectious peritonitis virus (FIPV) were reported as potential targets of teicoplanin and its chemical derivatives [2], [1], [2], [3]. Recently, additional studies have provided evidence that SARS-CoV-2, similarly to SARS-CoV, is a cathepsin L-dependent virus: in fact, these viruses require a multistep infection process including (i) receptor binding, (ii) change in spike (S) glycoprotein conformation, and finally (iii) cathepsin L proteolysis of the S protein, crucial for virus entry. Teicoplanin was found to specifically inhibit the activity of cathepsin L and potentially to play a critical role in blocking cell entry of the virus [2,6,7].