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Valaciclovir (Brand names: Zelitrex, Valtrex, among others) belongs to a group of medicines called antivirals. It works by killing or stopping the growth of viruses called herpes simplex (HSV), varicella zoster (VZV) and cytomegalovirus (CMV).

Valaciclovir can be used to treat shingles, herpes simplex infections of the skin and genital herpes. It is also used to help prevent these infections from returning.

Valaciclovir can be used also to treat cold sores, to prevent infection with cytomegalovirus after organ transplants and treat and prevent herpes simplex virus infections of the eye.






Valaciclovir is a prodrug, an esterified version of aciclovir that has greater oral bioavailability than aciclovir.
Valaciclovir is almost completely converted by esterases to acyclovir and L-valine.

Acyclovir is an acyclic guanine nucleoside analogue.
Acyclovir is phosphorylated by viral thymidine kinase to acyclovir monophosphate, the aciclovir affinity to viral thymidine kinase is much greater than for human thymidine kinase and therefore the phosphorylation reaction occurs more rapidly in cells infected with herpes virus than in normal cells.
Subsequently Acyclovir monophosphate is further converted to diphosphate and triphosphate by cellular enzymes.
Acyclovir-triphosphate enters in competition with deoxyguanosine triphosphate, and it's incorporation into viral DNA prevents DNA chain elongation due to the lack of 3'-hydroxyl group. The terminated DNA template containing acyclovir binds the enzyme and leads to irreversible inactivation of the DNA polymerase.

Herpesviruses encoding the thymidine kinase (herpes simplex and varicella-zoster) are much more sensitive to Valaciclovir than those that do not encode it (CMV and Epstein-Barr virus).


  • Adult Patients:
    • Herpes simplex (cold sores around the mouth)
    • Herpes Zoster (shingles)
    • Genital Herpes

  • Pediatric Patients
    • Herpes simplex (Herpes Labialis)
    • Chickenpox

[edit] DOSAGE

Begin use as soon as possible following the development of symptoms

  • Adult Patients:
    • Herpes simplex (Herpes Labialis): 2 grams every 12 hours for 1 day
    • Herpes Zoster (shingles): 1 gram 3 times daily for 7 days
    • Genital Herpes:
      • Initial episode: 1 gram twice daily for 10 days
      • Recurrent episodes: 500 mg twice daily for 3 days
      • Reduction of transmission: 500 mg once daily

  • Pediatric Patients
    • Herpes simplex (Herpes Labialis) in children aged greater than or equal to 12 years: 2 grams every 12 hours for 1 day
    • Chickenpox in children aged 2 to less than 18 years: 20 mg/kg 3 times daily for 5 days; not to exceed 1 gram 3 times daily


  • Hypersensitivity to valacyclovir or aciclovir


  • Precipitation of acyclovir in renal tubules may occur when the solubility (2.5 mg/mL) is exceeded in the intratubular fluid. Adequate hydration should be maintained for all patients (Take Valaciclovir with plenty of fluid)
  • Central nervous system adverse reactions (e.g., agitation, hallucinations, confusion, and encephalopathy): May occur in both adult and pediatric patients (with or without reduced renal function) and in patients with underlying renal disease who receive higher-than-recommended doses of Valaciclovir for their level of renal function. Elderly patients are more likely to have central nervous system adverse reactions. Use with caution in elderly patients and reduce dosage in patients with renal impairment


No clinically significant drug-drug or drug-food interactions with Valaciclovir are known


  • Pregnancy Category B (US). Valaciclovir should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
  • Caution should be exercised when Valaciclovir is administered to a nursing woman.


The most common adverse reactions are headache, dizziness, nausea, vomiting, and abdominal pain.


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