Antiviral drugs
Key examples
Common indications
- Treatment of acute episodes of herpesvirus infections, including herpes simplex (e.g. cold sores, genital ulcers, encephalitis) and varicella-zoster (e.g. chickenpox, shingles).
- Suppression of recurrent herpes simplex attacks where these are occurring at a frequency of 6 or more per year.
Mechanisms of action
- The herpesvirus family includes herpes simplex 1 and 2 and
varicella-zoster.
- These viruses contain double-stranded deoxyribonucleic
acid (DNA), which requires a herpes-specific DNA polymerase for the
virus to replicate.
- Aciclovir enters herpes-infected cells and inhibits the herpes-specific DNA polymerase, stopping further viral DNA synthesis and therefore replication.
Important adverse effects
- Common adverse effects of aciclovir include headache, dizziness, gastrointestinal disturbances and skin rash.
- Intravenous (IV) aciclovir commonly causes inflammation or phlebitis
at the injection site.
- Aciclovir is relatively water insoluble.
- During
high-dose IV therapy, delivery of a high concentration of aciclovir into
the renal tubules can cause precipitation, leading to crystal-induced acute renal failure.
- The risk of this can be minimised by ensuring good hydration and slowing the rate of infusion.
Warnings
- Aciclovir has no major contraindications.
- It does cross the placenta and is expressed in breast milk, so caution is advised in pregnant women and women who are breastfeeding.
However, as infections such as viral encephalitis, varicella pneumonia
and genital herpes carry significant risks to the mother and fetus, the
benefits of treatment in such circumstances are likely to outweigh its
risks.
- Aciclovir is excreted by the kidneys; the dose and/or frequency of administration should therefore be reduced in patients with severe renal impairment to prevent accumulation of the drug and subsequent toxicity.
Important interactions
- There are no clinically important drug interactions with aciclovir.
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