Unlike antibacterials (antibiotics) that kill bacteria, antivirals work by interfering with a virus’s ability to replicate, essentially “freezing” the infection so the immune system can catch up. They are highly specific, meaning a drug that works for the flu won’t work for a cold sore.
Here are 10 common antiviral tablets, their clinical uses, and what you should know about taking them.
Perhaps the most famous antiviral, this is a neuraminidase inhibitor used specifically for the influenza virus.
Primary Use: Treatment and prevention of Influenza A and B.
Typical Dose: 75mg twice daily for 5 days (for treatment) or once daily (for prevention).
Common Side Effects: Nausea, vomiting, headache, and rarely, confusion or unusual behavior in children.
A foundational antiviral used for the herpes family of viruses. It prevents the virus from synthesizing its DNA.
Primary Use: Cold sores, genital herpes, shingles, and chickenpox.
Typical Dose: 200mg to 800mg, taken 2 to 5 times daily depending on the severity.
Common Side Effects: Dizziness, tiredness, nausea, and skin sensitivity to sunlight.
Note. Dose reduction is important in AKI or CKD.
This is a “prodrug” of acyclovir. Once swallowed, the body converts it into acyclovir, allowing it to be absorbed much more efficiently.
Primary Use: Genital herpes (suppression or outbreaks) and shingles.
Typical Dose: 500mg to 1,000mg, taken 1 to 3 times a day.
Common Side Effects: Headache, stomach pain, and (in rare cases) kidney issues if not taken with enough water.
The primary oral treatment for COVID-19. Nirmatrelvir stops the virus from replicating, while Ritonavir acts as a “booster” to keep the drug in your system longer.
Primary Use: Mild-to-moderate COVID-19 in high-risk patients.
Typical Dose: Two 150mg tablets (Nirmatrelvir) and one 100mg tablet (Ritonavir) twice daily for 5 days.
Common Side Effects: Dysgeusia (a metallic or bitter taste in the mouth), diarrhea, and muscle aches.
This is a long-term antiviral used for chronic infections that incorporate themselves into the host’s DNA.
Primary Use: Chronic Hepatitis B and HIV-1 (as part of combination therapy).
Typical Dose: 300mg once daily.
Common Side Effects: Nausea, rash, and long-term concerns regarding bone density and kidney function.
Another COVID-19 antiviral, this drug works by introducing “errors” into the virus’s genetic code until it can no longer function.
Primary Use: COVID-19 treatment when other options (like Paxlovid) aren’t suitable.
Typical Dose: 800mg (four 200mg capsules) every 12 hours for 5 days.
Common Side Effects: Diarrhea, dizziness, and nausea.
Similar to valacyclovir, this is a prodrug that turns into penciclovir in the body to fight herpes viruses.
Primary Use: Shingles (Herpes Zoster) and recurrent cold sores.
Typical Dose: 250mg to 500mg, taken 2 to 3 times a day for 7 days.
Common Side Effects: Headache, nausea, and occasional drowsiness.
A potent nucleoside analog specifically designed to stop the Hepatitis B virus from multiplying.
Primary Use: Chronic Hepatitis B infection with evidence of liver inflammation.
Typical Dose: 0.5mg to 1mg once daily on an empty stomach.
Common Side Effects: Headache, fatigue, and dizziness.
A newer “single-dose” flu medication. Unlike Tamiflu, which requires 5 days of pills, this is usually a one-and-done treatment.
Primary Use: Acute, uncomplicated influenza (Flu).
Typical Dose: A single 40mg or 80mg dose (depending on body weight).
Common Side Effects: Diarrhoea, bronchitis, and nausea.
A key component in many HIV treatment regimens (often found in combination tablets like Triumeq).
Primary Use: Management of HIV infection.
Typical Dose: 600mg daily (or 300mg twice daily).
Common Side Effects: Nausea, insomnia, and fatigue.
Important: This drug requires a genetic test (HLA-B*5701) before use because of a risk for a severe hypersensitivity reaction.
| Virus Target | Common Tablets | Key Distinction |
| Influenza (Flu) | Oseltamivir, Baloxavir | Best if started within 48 hours of symptoms. |
| Herpes / Shingles | Acyclovir, Valacyclovir | Valacyclovir is absorbed better than Acyclovir. |
| COVID-19 | Paxlovid, Molnupiravir | Must be started within 5 days of symptoms. |
| Hepatitis B | Tenofovir, Entecavir | Usually taken daily for long-term suppression. |
For acute viruses like the flu or shingles, antivirals are most effective when started within 48 hours of the first symptoms appearing. If you wait too long, the virus has already replicated so much that the medication won’t be able to significantly shorten the illness.
Are you looking for information on a specific viral symptom, or is this for general reference?
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