"Lopinavir and ritonavir are both protease inhibitors developed specifically to treat HIV. Remdesivir, on the other hand, is a broad-spectrum antiviral. It was initially developed to treat Ebola, but it is a nucleotide analog that mimics adenosine, one of the building blocks of any RNA virus’s genome. Drugs that act as nucleotide analogs interfere with the RNA-dependent RNA polymerase, the enzyme that viruses use to copy their genomes, says Matthias Götte, a biochemist at the University of Alberta. 'If you target this enzyme the virus cannot replicate anymore, so it’s a very logical target to begin with.'"