EXOGENOUS PATHOGENS AND TOXINS 557Zanamivir (9.31) and oseltamivir (9.32) are neuraminidase inhibitors. Neuraminidase is
an essential viral glycoprotein, playing a central role in viral replication and release. These
agents work against both influenza A and B. Zanamivir is given intranasally, 10 mg twice
daily for 5 days. Peramivir (9.33, figure 9.2) is another selective influenza neuraminidase
inhibitor that has been under development. The synthesis of peramivir is shown in figure 9.2.
Among drugs with uncertain modes of action, ribavirin (9.34) is not exactly a
nucleotide since the purine ring is replaced by a triazole. It is active against HSV-1 and
-2, hepatitis, and perhaps influenza viruses. It seems to have multiple effects on viral
replication, blocking RNA synthesis and mRNA capping. Rifampin, an antibacterial, is
effective against DNA viruses like HSV and the smallpox virus. It also prevents the
virus-induced transformation of cells to malignant forms. Bleomycin (9.35), primarily
an antitumor agent, also shows some activity as an antiviral agent.
An antiviral (and anticancer) compound very much in the news media is interferon,
a peptide consisting of about 150 amino acids (discussed in chapter 6). It is produced by
most cells upon viral infection or a challenge by interferon-inducing agents, and protects