Antivirals

Written by Rosemary Osuoha, B.Pharm
Last updated on july 3, 2025

Medically Reviewed By: Oladeji Robert B.Pharm, MPSN

Edited By: Ugwuleke Clement B.Pharm, MPSN

Antiviral drugs are medications specifically developed to treat infections caused by viruses. They work by interfering with a virus's ability to replicate, helping to reduce disease severity, shorten healing time, and prevent complications.

Common Viral Diseases Treated by Antivirals

• Influenza (Flu)
• Herpes simplex (oral and genital)
• Varicella-zoster (chickenpox, shingles)
• HIV/AIDS
• Hepatitis B and C
• Respiratory syncytial virus (RSV)

Common Antiviral Drugs

Major Classes of Antiviral Drugs

1. Neuraminidase Inhibitors

Used primarily for influenza; they reduce viral spread.

• Oseltamivir (Tamiflu®)
• Zanamivir (Relenza®)
• Peramivir (Rapivab®)

2. Nucleoside/Nucleotide Analogues

Block viral DNA/RNA synthesis.

• Acyclovir, Valacyclovir (Herpes simplex & VZV)
• Tenofovir, Lamivudine (Hepatitis B, HIV)
• Remdesivir (SARS-CoV-2)

3. Protease Inhibitors

Prevent viral protease enzymes from processing viral proteins.

• Lopinavir/Ritonavir, Atazanavir (HIV treatment)
• Simeprevir (Hepatitis C)

4. Polymerase Inhibitors

Inhibit viral polymerase enzyme activity.

• Remdesivir (RNA polymerase inhibitor for COVID-19)
• Favipiravir (Influenza, off-label use)

5. Integrase Inhibitors

Block integration of viral DNA into the host genome:

• Raltegravir, Dolutegravir (HIV)

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Important Considerations

• Drug resistance can occur—adherence is essential.
• Side effects may include nausea, liver function changes, kidney effects.
• Drug interactions are common—check with your provider.
• Some require regular laboratory monitoring during use.

Antivirals are often part of combination therapy, especially for HIV and hepatitis. They are most effective when started early in the infection or as prophylaxis for high-risk individuals.

Common Types of Antivirals:

There are different classes of antiviral medications, each tailored to combat specific viruses:

1. Anti-Influenza Agents

Used to treat and prevent the flu:

• Oseltamivir (Tamiflu)
• Zanamivir (Relenza)
• Baloxavir marboxil (Xofluza)

These drugs are most effective when taken within the first 48 hours of symptom onset.

2. Antiretrovirals for HIV

These drugs are used in combination (known as antiretroviral therapy or ART) to manage HIV:

• Tenofovir
• Emtricitabine
• Dolutegravir
• Efavirenz

ART helps reduce the viral load to undetectable levels, improving quality of life and reducing the risk of transmission.

3. Anti-Herpes Medications

These treat herpes simplex virus (HSV) infections and varicella-zoster virus (chickenpox and shingles):

• Acyclovir
• Valacyclovir
• Famciclovir

They help reduce outbreaks and speed up healing.

4. Hepatitis Antivirals

Used to manage chronic hepatitis B and C:

• Sofosbuvir
• Ledipasvir
• Entecavir
• Tenofovir

Some regimens can cure hepatitis C in 8–12 weeks.

5. COVID-19 Antivirals

Developed in response to the coronavirus pandemic:

• Paxlovid (nirmatrelvir/ritonavir)
• Remdesivir

These antivirals help reduce hospitalizations and severe symptoms if started early.

When Are Antivirals Used?

Antivirals are prescribed in various scenarios:

• Treatment: To reduce the duration and severity of symptoms in an active infection.
• Prophylaxis: To prevent infection after exposure (e.g., HIV post-exposure prophylaxis).
• Chronic Management: To control long-term viral infections and prevent complications (e.g., HIV, hepatitis B/C).

Limitations and Side Effects

Antivirals are powerful but not always a cure. Some viruses, like HIV and herpes, remain in the body for life even with treatment. Others, like hepatitis C, can be cured with certain antiviral regimens.

Common side effects include:

• Nausea
• Diarrhea
• Headache
• Fatigue

Rare but serious effects may include liver toxicity, allergic reactions, or resistance development if not taken as prescribed.

How Do Antivirals Work?

Viruses replicate by entering healthy cells and hijacking their machinery to make more virus copies. Antiviral drugs target specific parts of this cycle to disrupt the virus’s ability to spread. Depending on the drug, antivirals can:

• Prevent the virus from entering cells.
• Inhibit enzymes the virus needs to replicate.
• Stop viral genetic material from being copied.
• Prevent the release of new viral particles from infected cells.

Because viruses mutate frequently, some antivirals must be used in combination to prevent resistance and maintain effectiveness.