Aciclovir
A guanosine analog antiviral for herpes simplex and varicella-zoster: cold sores, genital herpes, shingles, chickenpox and encephalitis.
Also called acyclovir (US name) or ACV (abbreviation).
Drug card
- How it works
- Blocking herpesvirus DNA polymerase after activation by viral thymidine kinase
- Used for
- Herpes simplex, from cold sores to encephalitis (IV)
- Shingles (herpes zoster)
- Chickenpox
- Herpes simplex eye infections (ointment)
- Known for
- Kidney injury from crystals, mainly with IV use
- Confusion, hallucinations, seizures, encephalopathy
- Its name
- -vir means an antiviral; -ciclovir means an antiherpes nucleoside analogue
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does aciclovir work?
Viral thymidine kinase gives it its first phosphate, so it is activated mainly in infected cells; the triphosphate blocks viral DNA polymerase and ends the DNA chain. It is more active against herpes simplex than varicella-zoster, as the simplex enzyme phosphorylates it better. It comes as tablets, cream, eye ointment and an IV infusion.
Like other antiherpes nucleoside analogues: These guanosine analogs are switched on mainly in infected cells: the thymidine kinase of herpes simplex or varicella-zoster virus adds the first phosphate, and cell enzymes make the triphosphate. That triphosphate competes for viral DNA polymerase, is built into the growing viral DNA and ends the chain. Most resistant viruses lack a working thymidine kinase.
Uses
What is aciclovir used for?
- Herpes simplex, from cold sores to encephalitis (IV)
- Shingles (herpes zoster)
- Chickenpox
- Herpes simplex eye infections (ointment)
Side effects
Side effects of aciclovir
- Kidney injury from crystals, mainly with IV useKnown forSerious
- Confusion, hallucinations, seizures, encephalopathyKnown forSerious
- Nausea and vomiting
- Diarrhea
- Headache
- Vein inflammation at the IV site
- Rash and itching
- Severe skin reactions: SJS, TENSerious
- TTP/HUS in immunocompromised patientsSerious
- Hepatitis and jaundiceSerious
- Low blood countsSerious
- Anaphylaxis and angioedemaSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Reduce the dose in kidney impairment; older people are most prone to brain and kidney toxicity.
- IV use: keep the patient well hydrated and infuse over at least 1 hour, so crystals do not form in the kidneys.
- Extra care with other nephrotoxic drugs; probenecid raises aciclovir levels.
- Treatment works best started early, as soon as possible after a shingles or chickenpox rash appears.
Good to know: Aciclovir is the INN; acyclovir is the US name. Its prodrug valaciclovir gives several times more aciclovir in the blood after an oral dose.
Remember it
A way to remember it
The virus loads its own trap.
Viral thymidine kinase adds the first phosphate, so aciclovir is activated mainly in infected cells, where it then jams the viral DNA polymerase. Viruses that lose thymidine kinase escape it.
Written for biofideX
Its name
-vir means antiviral
Sub-stems name the target: -ciclovir, -amivir, -fovir, -tegravir, -navir, -buvir, -virine (NNRTIs). Lamivudine and zidovudine are antivirals without it.
-ciclovir means antiherpes nucleoside analogue
Aciclovir, valaciclovir, ganciclovir and penciclovir share it. The US names of the first two are acyclovir and valacyclovir.
- Every drug name stem
Its class
Antiherpes nucleoside analogues
Other antiherpes nucleoside analogues with a card:
Easily mixed up with nucleoside reverse transcriptase inhibitors and NS5B polymerase inhibitors.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Acyclovir capsules: label (DailyMed)
- Acyclovir sodium injection: label (DailyMed)
- Acyclovir (NCI Thesaurus)
- Aciclovir (NHS)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Antivirals
Aciclovir is one of 10 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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