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[Pharmacology](https://durgical.com/en/pharmacology/) · Class

# Other antivirals

Antivirals that do not fit the herpes, flu, hepatitis B or HIV groups: ribavirin and the COVID-19 drugs remdesivir and nirmatrelvir with ritonavir.

Updated 2026-11-01

## What they are

A mixed group. Ribavirin is an old broad-spectrum nucleoside analogue, now used mainly with other hepatitis C drugs. Remdesivir and nirmatrelvir-ritonavir treat COVID-19: nirmatrelvir-ritonavir is oral for outpatients at high risk, and remdesivir is intravenous for hospitalized or high-risk patients. Molnupiravir, favipiravir and tecovirimat (for mpox) belong here too.

## Mechanism of action

Each acts on a different step. Ribavirin depletes guanosine nucleotides by inhibiting IMP dehydrogenase, increases viral mutations and may inhibit the viral polymerase. Remdesivir is a nucleotide prodrug whose triphosphate is built into the viral RNA by the coronavirus RNA polymerase and stops synthesis a few nucleotides later. Nirmatrelvir blocks the SARS-CoV-2 main protease (Mpro), which cuts the viral polyprotein; ritonavir is added only to slow its breakdown.

Target: Viral RNA polymerases, SARS-CoV-2 main protease, IMP dehydrogenase

## Key points

- Ribavirin causes haemolytic anaemia and is strongly teratogenic: pregnancy is avoided in women and in the partners of men for 6 months after the last dose.
- Ribavirin is never used alone for hepatitis C.
- Nirmatrelvir-ritonavir: ritonavir strongly inhibits CYP3A, so every medicine the patient takes is checked for interactions.
- Nirmatrelvir-ritonavir is started within 5 days of COVID-19 symptoms in people at high risk.
- Remdesivir: infusion-related reactions and raised transaminases; it is not given with chloroquine or hydroxychloroquine.

## Drugs in this class

- [**Ribavirin** An old broad-spectrum antiviral, now used with other hepatitis C drugs. It causes haemolytic anaemia and is strongly… Inosine monophosphate dehydrogenase (IMPDH) and viral RNA polymerase](https://durgical.com/en/pharmacology/ribavirin/)
- [**Remdesivir** An intravenous COVID-19 antiviral that blocks the coronavirus RNA polymerase. It needs liver tests and watch for… SARS-CoV-2 RNA-dependent RNA polymerase (nsp12)](https://durgical.com/en/pharmacology/remdesivir/)
- [**Nirmatrelvir + ritonavir** An oral COVID-19 treatment for people at high risk, started within 5 days of symptoms. Ritonavir boosts it and causes… SARS-CoV-2 main protease (Mpro, 3CL protease)](https://durgical.com/en/pharmacology/nirmatrelvir-ritonavir/)

## Others in the class

- Molnupiravir
- Favipiravir
- Tecovirimat

## Test yourself

Think of the answer, then tap the question to see it.

## Why is ritonavir included with nirmatrelvir?

It inhibits CYP3A, which slows the breakdown of nirmatrelvir and keeps its levels high; it has no useful activity against SARS-CoV-2 itself.

## What is the main toxicity of ribavirin?

Haemolytic anaemia, which can worsen heart disease; it is also strongly teratogenic.

## How does remdesivir stop coronavirus RNA synthesis?

Its triphosphate is built into the new RNA by the viral polymerase, which adds only a few more nucleotides and then stops.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 62 (McGraw Hill, 2023); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=J05AX) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=J05AB) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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