Chapter 43: Drugs for the Treatment of Viral Infections

Drugs for the Treatment of Viral Infections exploration of antiviral pharmacology details the therapeutic strategies used to combat various viral pathogens by disrupting their unique replication cycles. Since viruses function as obligate intracellular parasites, the focus is on medications that can inhibit viral processes without causing excessive harm to the host cell. The chapter begins with the management of herpesvirus infections, emphasizing nucleoside analogs like acyclovir, famciclovir, and their respective prodrugs, valacyclovir and valganciclovir. These agents typically require activation by viral kinases to ultimately inhibit viral DNA polymerase, whereas non-nucleoside options like foscarnet block replication without metabolic activation. Moving to the treatment of Human Immunodeficiency Virus (HIV), the text outlines the evolution of highly active antiretroviral therapy (HAART). This multifaceted approach combines different classes, including nucleoside and non-nucleoside reverse transcriptase inhibitors (NRTIs and NNRTIs), protease inhibitors (PIs) that prevent viral maturation, and integrase strand transfer inhibitors (INSTIs) that stop the virus from merging its genome with the host's DNA. Additionally, fusion and entry inhibitors provide vital alternatives for resistant strains. For influenza, neuraminidase inhibitors such as oseltamivir prevent the spread of virions, while the newer agent baloxavir targets the viral endonuclease. The discussion also covers the significant advancements in treating viral hepatitis, contrasting the long-term suppression strategies for Hepatitis B (HBV) with the high-cure-rate direct-acting antivirals (DAAs) for Hepatitis C (HCV) that target specific nonstructural proteins. Broad-spectrum agents like ribavirin and the immune-boosting peginterferon alfa are also analyzed alongside monoclonal antibodies like palivizumab for respiratory syncytial virus (RSV). The chapter concludes with specialized treatments for smallpox and therapeutic responses to the SARS-CoV-2 pandemic, including the use of remdesivir and dexamethasone.