Antiviral Agents

Antiviral Agents

What Are Antiviral Agents?

Antiviral agents are medicines used to control or treat viral infections.
They don’t kill the virus directly, but stop or slow down its growth.
Some work on a specific virus, while broad-spectrum antivirals work against many types.
These drugs are approved by health authorities (like the FDA) for managing viral diseases.

1. Acyclovir

Used for: Herpes virus infections.
Taken as: Tablets, capsules, or IV (slow infusion).
How it works:

The virus converts acyclovir into its active form inside infected cells.
This active form blocks viral DNA production, stopping the virus from multiplying.

Resistance: More common in people with weak immune systems.
Common effects: Mild nausea, headache, tiredness, or confusion.

2. Ribavirin

Used for: Hepatitis C (often combined with interferon).
How it works:

Acts like a “fake” building block of viral RNA.
Stops the virus from copying its genetic material.

Resistance: Rare, but can happen in Hepatitis C viruses.
Common effects: Headache, nausea, tiredness, and mild flu-like symptoms.

3. Amantadine

Used for: Influenza A and sometimes Parkinson’s disease.
How it works:

Blocks the virus from releasing its genetic material inside host cells.
Also prevents the virus from assembling new particles.

Resistance: Can occur due to viral mutations.
Common effects: Dizziness, trouble sleeping, nausea, and confusion.

4. Zanamivir

Used for: Influenza (flu) infections.
How it works:

Blocks the viral enzyme neuraminidase, which helps the virus leave the host cell.
This stops the virus from spreading to new cells.

Resistance: Rare but possible through amino acid changes in the virus.
Common effects: Headache, cough, nausea, and sore throat.

5. Entecavir

Used for: Chronic Hepatitis B virus (HBV) infection.
How it works:

Stops the virus from making copies of its DNA.
Lowers the amount of virus in the blood.

Resistance: Very low.
Common effects: Headache, dizziness, nausea, or mild liver discomfort.

6. Tecovirimat

Used for: Smallpox and monkeypox viruses.
How it works:

Stops the virus from leaving infected cells, preventing it from spreading.

Resistance: Rare, but may occur with viral mutations.
Common effects: Mild stomach upset, tiredness, or skin redness.

7. Lamivudine

Used for: HIV and Hepatitis B infections.
How it works:

Blocks an enzyme called reverse transcriptase, stopping the virus from copying itself.
Slows disease progression by preventing new virus formation.

Resistance: May occur due to genetic changes in the virus.
Common effects: Fatigue, headache, diarrhea, or runny nose.

8. Pleconaril

Used for: Viruses like enteroviruses and rhinoviruses (common cold family).
How it works:

Fits into the viral shell and blocks the virus from attaching to host cells.
Prevents the virus from uncoating and releasing its RNA.

Resistance: Some viruses can become less sensitive due to structural changes.
Common effects: Mild headache, nausea, and stomach discomfort.

9. Valacyclovir

Used for: Shingles, cold sores, and genital herpes.
How it works:

Converts to acyclovir inside the body, which blocks viral DNA synthesis.
Prevents the virus from replicating further.

Resistance: Rare, but more likely in patients with weak immunity.
Common effects: Nausea, dizziness, headache, or mild rash.

Summary Table

Drug	Used Against	How It Works	Common Effects
Acyclovir	Herpes virus	Stops viral DNA formation	Nausea, headache
Ribavirin	Hepatitis C	Blocks viral RNA synthesis	Fatigue, flu-like signs
Amantadine	Influenza A	Blocks viral entry	Dizziness, nausea
Zanamivir	Flu virus	Stops virus from spreading	Cough, headache
Entecavir	Hepatitis B	Blocks DNA replication	Fatigue, nausea
Tecovirimat	Smallpox, monkeypox	Prevents virus release	Mild stomach upset
Lamivudine	HIV, HBV	Blocks reverse transcriptase	Diarrhea, headache
Pleconaril	Enteroviruses, rhinoviruses	Blocks virus binding/uncoating	Headache, nausea
Valacyclovir	Herpes, shingles	Inhibits DNA polymerase	Rash, dizziness

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