Introduction to Antiviral Agents,   Antiviral agents are a class of pharmaceuticals designed to treat viral infections by targeting specific stages of the viral life cycle. Unlike antibiotics, which combat bacterial infections, antivirals are tailored to disrupt viral replication without harming host cells. Their mechanisms vary, including blocking viral entry into host cells, inhibiting viral enzymes (like proteases or polymerases), or preventing the assembly and release of new virions. These drugs serve dual purposes: prophylaxis (preventing infection, e.g., pre-exposure HIV prophylaxis) and treatment of active infections. Notable examples include oseltamivir (Tamiflu) for influenza, acyclovir for herpesviruses, and antiretrovirals like tenofovir for HIV. The COVID-19 pandemic highlighted antivirals such as remdesivir and nirmatrelvir/ritonavir (Paxlovid), underscoring their critical role in emerging diseases. Challenges in antiviral development include viral resistance due to rapid mutation, the complexity of creating broad-spectrum agents against diverse viruses (e.g., RNA vs. DNA viruses), and latent infections (e.g., herpesviruses) that evade treatment. Despite this, antivirals offer significant benefits: reducing disease severity, shortening duration, and curbing transmission. They complement vaccines, which prevent infection but are less effective post-exposure. Advances in combination therapies (e.g., HAART for HIV) and targeted drug design continue to enhance efficacy. However, antivirals are not a panacea; their success hinges on timely administration and ongoing innovation to address resistance. As viral threats evolve, antivirals remain pivotal in global health strategies, bridging prevention and cure in the fight against infectious diseases. 

Side effects of herpesvirus antivirals 

: Acyclovir/ Valacyclovir/ Famciclovir/ Ganciclovir Valganciclovir

 Nausea and vomiting - Diarrhea - Headache (especially with Acyclovir, Valacyclovir, and Famciclovir 

Side Effects of Influenza Antivirals

 They are

 Oseltamivir/ Zanamivir

 - Headache - Nausea (more common with oseltamivir) -Diarrhea -Dizziness 

Side Effects of Hepatitis C virals 

They are

 Ribavirin Sofosbuvir/ Ledipasvir Simeprevir

 Fatigue - Headache(in Sofosbuvir, Ledipasvir) - Nausea (in Ribavirin, Sofosbuvir, Simeprevir)