Penciclovir
Anti-herpesvirus agents
Anti-herpesvirus agents
A topical antiviral cream for cold sores (herpes labialis). It is the active form of famciclovir.
Quick facts
- Group
- Anti-herpesvirus agents
- Target
- Viral thymidine kinase (activation) and viral DNA polymerase
- Used for
- Recurrent cold sores
- Key effects
- Headache
- Monitor
- Healing of the lesion
- ATC
- D06BB06
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows penciclovir in herpes simplex virus 1 thymidine kinase, the enzyme that starts its activation.
Penciclovir is an acyclic guanine nucleoside analogue. In infected cells the viral thymidine kinase phosphorylates it, and cellular kinases make penciclovir triphosphate, which competes with the natural nucleotide at the viral DNA polymerase. It is weaker than aciclovir triphosphate at the enzyme but reaches higher levels and stays much longer in infected cells. It is not an obligate chain terminator but slows DNA elongation. Thymidine kinase-deficient, aciclovir-resistant strains are cross-resistant.
- Viral thymidine kinase phosphorylates penciclovir
- Cell kinases form penciclovir triphosphate
- It inhibits the viral DNA polymerase
- It stays long in infected cells
Indications
- Recurrent cold sores (herpes labialis) on the lips and face in adults Genital herpes (herpes simplex infection) →
Adverse effects
Common
- Irritation or redness at the application site
- Headache
Contraindications
- Hypersensitivity to penciclovir
Key interactions
- Other medicines
- No clinically important interactions are described for the cream
What is monitored
- Healing of the lesion; spread or no improvement prompts review
Administration and safety
- Applied only to lesions on the lips and face, starting at the first symptoms
- Hands are washed before and after application
Pregnancy and breastfeeding
Safety in pregnancy has not been established; topical use gives little exposure, and benefit and risk are weighed.
Nursing care
- Teach to start at the first tingling or burning
- Explain that it shortens symptoms but does not cure herpes
- Teach to avoid touching the lesion and kissing during an outbreak
- Ask about allergy to aciclovir or famciclovir
Pharmacokinetics
- Absorption
- Poor oral absorption, so it is used on the skin; famciclovir is the oral prodrug
- Elimination
- Penciclovir that reaches the blood is excreted mostly unchanged in the urine
Test yourself
Think of the answer, then tap the question to see it.
Why is penciclovir used as a cream rather than by mouth?
It is poorly absorbed orally; the oral route uses its prodrug famciclovir.
Which enzyme starts penciclovir activation?
The viral thymidine kinase.
Are thymidine kinase-deficient, aciclovir-resistant herpes strains sensitive to penciclovir?
No. They are cross-resistant, because penciclovir also needs the viral thymidine kinase.
Connections
← Back to the class: Anti-herpesvirus agents
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Penciclovir Cream: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); CRYSTAL STRUCTURE OF THYMIDINE KINASE FROM HERPES SIMPLEX VIRUS TYPE I COMPLEXED WITH PENCICLOVIR (RCSB Protein Data Bank, 1999).
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Representative model, for educational purposes only.