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
Drugs in this class
- RibavirinAn 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
- RemdesivirAn 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)
- Nirmatrelvir + ritonavirAn 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)
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.
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 (WHO Collaborating Centre for Drug Statistics Methodology, 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.