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.

• AciclovirAciclovir is the INN; acyclovir is the US name. Its prodrug valaciclovir gives several times more aciclovir in the blood after an oral dose.
• ValaciclovirValaciclovir is the INN; valacyclovir is the US name. Its better absorption lets it be taken fewer times a day than aciclovir.

• Herpes simplex: cold sores, genital herpes, encephalitis
• Shingles (herpes zoster)
• Chickenpox
• Herpes simplex eye infections

• Kidney injury from drug crystalsKnown forSerious
• Confusion, hallucinations, encephalopathyKnown forSerious
• Headache
• Nausea and vomiting
• Diarrhea
• Rash, including rash in sunlight
• Severe skin reactions: SJS, TENSerious
• TTP/HUS in immunocompromised patientsSerious
• Raised liver enzymes and hepatitisSerious

What the class has in common. Each drug's card has its own, and Known for marks what an exam expects you to know.

• Reduce the dose in kidney impairment; older people are most prone to kidney and brain toxicity.
• Keep patients well hydrated, as the drug can crystallize in the kidney tubules.
• Take extra care with other nephrotoxic drugs.
• Start early: for shingles, benefit is shown only when treatment begins within 72 hours of the rash.

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.