Viruses are tiny infectious agents that depend completely on human cells for survival and multiplication. Because they use our own cell machinery, developing safe antiviral drugs is more challenging than creating antibiotics. Antiviral agents work by blocking key steps of viral entry, replication, protein formation, or release from host cells.
General Principles of Antiviral Therapy
- Most antivirals are virus-specific and work on only certain infections.
- They are more effective when given early in the infection.
- They are usually virolstatic—they stop viral growth but may not kill the virus completely.
Major Groups of Antiviral Agents
1. Anti-Herpes Virus Drugs
Used for herpes simplex virus (HSV), varicella-zoster virus (VZV), and cytomegalovirus (CMV).
Common Drugs
- Acyclovir
- Valacyclovir
- Famciclovir
- Ganciclovir (for CMV)
- Foscarnet
Mechanism
Acyclovir and related drugs inhibit viral DNA polymerase, stopping viral DNA synthesis.
Uses
- Cold sores, genital herpes
- Shingles (VZV)
- CMV infections (ganciclovir)
Side Effects
- Nausea, headache
- Kidney toxicity at high doses
2. Anti-Influenza Drugs
Adamantanes
- Amantadine
- Rimantadine
Block viral uncoating in influenza A. Rarely used now due to resistance.
Neuraminidase Inhibitors
- Oseltamivir (Tamiflu)
- Zanamivir
- Peramivir
These drugs stop viral release from infected cells and shorten the course of flu if given early.
3. Anti-Hepatitis Drugs
For Hepatitis B (HBV)
- Tenofovir
- Entecavir
- Interferon-alpha
For Hepatitis C (HCV)
Modern treatment uses direct-acting antivirals (DAAs):
- Sofosbuvir
- Ledipasvir
- Velpatasvir
These drugs cure most cases of hepatitis C.
4. Anti-HIV (Antiretroviral) Drugs
HIV therapy uses combinations of drugs called HAART (Highly Active Antiretroviral Therapy). HIV drugs act on different stages of the virus life cycle.
Main Classes
1. NRTIs (Nucleoside Reverse Transcriptase Inhibitors)
- Zidovudine (AZT)
- Lamivudine (3TC)
- Tenofovir
2. NNRTIs (Non-Nucleoside Reverse Transcriptase Inhibitors)
- Efavirenz
- Nevirapine
3. Protease Inhibitors (PIs)
- Lopinavir
- Ritonavir
4. Integrase Inhibitors
- Raltegravir
- Dolutegravir
5. Entry/Fusion Inhibitors
- Enfuvirtide
- Maraviroc
Interferons
Interferons are natural proteins that boost the body’s immune response against viruses.
Uses
- Hepatitis B and C
- Certain cancers
- HPV warts
Side Effects
- Flu-like symptoms
- Depression
- Fatigue
General Side Effects of Antiviral Drugs
- Nausea and vomiting
- Headache
- Liver enzyme elevation
- Kidney problems (especially acyclovir)
- Blood disorders (some anti-HIV drugs)
Resistance to Antiviral Drugs
- Mutations in viral enzymes
- Incomplete or irregular therapy (especially in HIV)
- High viral replication rate
Combination therapy is used in HIV and hepatitis C to prevent resistance.
Detailed Notes:
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