[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › Anti-herpesvirus agents [Pharmacology](https://durgical.com/en/pharmacology/) · Class # Anti-herpesvirus agents Antivirals that stop herpesviruses (herpes simplex, varicella-zoster, cytomegalovirus) from copying their DNA. They control outbreaks but do not cure. Updated 2026-11-01 ## What they are Medicines for infections by herpesviruses: herpes simplex (cold sores, genital herpes, encephalitis), varicella-zoster (chickenpox, shingles) and cytomegalovirus (CMV) in transplant recipients and people with advanced HIV. The virus stays latent in the body, so these drugs treat episodes or suppress them; they do not remove the virus. ## Mechanism of action Almost all of them end up blocking the viral DNA polymerase. Aciclovir, valaciclovir and famciclovir (penciclovir) are first phosphorylated by the viral thymidine kinase, so they act mainly in infected cells. Ganciclovir and valganciclovir are activated in CMV by the viral kinase UL97. Cidofovir is a nucleotide that only needs cellular kinases, and foscarnet binds the polymerase directly at its pyrophosphate site, so both still work when the viral kinase is missing or mutated. Target: Viral DNA polymerase (activated by viral thymidine kinase or UL97 kinase) ## Key points - Aciclovir needs the viral thymidine kinase: thymidine kinase-deficient strains are resistant, and foscarnet (or cidofovir) is then used. - IV aciclovir can crystallize in the renal tubules: it is infused slowly with good hydration; it can also cause confusion or seizures. - Ganciclovir and valganciclovir: myelosuppression (neutropenia) is the main toxicity; CMV activates them through UL97. - Foscarnet: nephrotoxicity and low ionized calcium and magnesium, with seizures. Cidofovir: nephrotoxicity, given with probenecid and saline. - Herpes simplex encephalitis: IV aciclovir is started as soon as it is suspected. ## Drugs in this class - [**Aciclovir** The classic antiviral for herpes simplex and varicella-zoster. Given early, it shortens outbreaks; IV it treats herpes… Viral DNA polymerase (herpes simplex and varicella-zoster)](https://durgical.com/en/pharmacology/aciclovir/) - [**Valaciclovir** An oral prodrug that the body turns into aciclovir. It is much better absorbed, so it is taken less often for herpes… Viral DNA polymerase (through its active form, aciclovir)](https://durgical.com/en/pharmacology/valaciclovir/) - [**Famciclovir** An oral prodrug of penciclovir for shingles and herpes simplex. Its active form stays inside infected cells for many… Viral thymidine kinase (activation) and viral DNA polymerase](https://durgical.com/en/pharmacology/famciclovir/) - [**Ganciclovir** An intravenous antiviral for cytomegalovirus (CMV) in transplant recipients and people with AIDS. Its main danger is… CMV DNA polymerase (activated by the viral UL97 kinase)](https://durgical.com/en/pharmacology/ganciclovir/) - [**Valganciclovir** The oral prodrug of ganciclovir. It prevents and treats cytomegalovirus (CMV) disease and can lower all blood cell… CMV DNA polymerase (through ganciclovir, activated by UL97)](https://durgical.com/en/pharmacology/valganciclovir/) - [**Cidofovir** An intravenous antiviral for CMV retinitis in AIDS. It works without the viral kinase but is very toxic to the kidneys. Viral DNA polymerase (CMV)](https://durgical.com/en/pharmacology/cidofovir/) - [**Foscarnet** An intravenous antiviral for resistant herpes simplex and CMV. It blocks the viral polymerase directly but harms the… Viral DNA polymerase (pyrophosphate-binding site)](https://durgical.com/en/pharmacology/foscarnet/) ## Others in the class - Penciclovir (topical) - Letermovir - Maribavir - Brincidofovir - Trifluridine (ophthalmic) ## Test yourself Think of the answer, then tap the question to see it. ## Which viral enzyme must phosphorylate aciclovir before it can act? The viral thymidine kinase. That is why it acts mainly in infected cells and why thymidine kinase-deficient strains resist it. ## Which two drugs still work against aciclovir-resistant, thymidine kinase-deficient herpes simplex? Foscarnet, which binds the polymerase directly, and cidofovir, which is phosphorylated only by cellular enzymes. ## What is the main dose-limiting toxicity of ganciclovir? Bone marrow suppression, above all neutropenia, plus anaemia and thrombocytopenia. ## Which electrolyte problems are typical of foscarnet? Low ionized calcium, low magnesium, low potassium and changes in phosphate, which can cause tingling around the mouth and seizures. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/classes/anti-herpesvirus-agents/) [← All of pharmacology](https://durgical.com/en/pharmacology/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [Herpes simplex virus](https://www.who.int/news-room/fact-sheets/detail/herpes-simplex-virus) (World Health Organization, 2025); 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=J05AB) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/classes/anti-herpesvirus-agents/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/classes/anti-herpesvirus-agents/