VALACYCLOVIR (Valtrex): What is used for?

What is Valacyclovir?

Valacyclovir (Valaciclovir) is a drug used to treat Herpes zoster, Herpes simplex, Cold sores and HSV. The product ingredient is Valacyclovir hydrochloride (hcl).

The brand name of Valaciclovir in the United States is Valtrex.

Mechanism of action (MOA) of Valacyclovir

Antiviral, inhibits DNA synthesis and blocks viral replication.

Therapeutic indications, uses and benefits of Valacyclovir

Treatment of herpes zoster and ophthalmic zoster in immunocompetent adults.

Treatment of herpes zoster in adults with mild to moderate immunosuppression.

Suppression and treatment of HSV infections of the skin and mucous membranes, including: treatment of the first episode of genital herpes in immunocompetent adults and adolescents and immunocompromised adults, treatment of genital herpes recurrences in immunocompetent adults and adolescents and immunocompromised adults, and suppression of recurrent genital herpes in immunocompromised adults and adolescents and immunocompromised adults and adolescents.

Suppression and treatment of recurrent ocular infections by HSV in immunocompetent adults and adolescents and in immunocompromised adults; prophylaxis of CMV infection and for diseases after solid organ transplantation in adults and adolescents.

Posology of Valacyclovir

Herpes zoster: adults: 1 g/8 h, 7 days.
Herpes simplex: adults and adolescents > 12 years: 500 mg/12 h; severe initial episode: 10 days; recurrences: 5 days.
Cold sores: adults and adolescents: 2 g/12 h, 1 day.
Treatment of HSV in immunocompromised patients: 1 g/12 h, 5 days; in severe cases: 10 days.
Suppression of recurrent HSV infections in adults and adolescents ≥ 12 years: 500 mg/day; in immunocompromised patients: 500 mg/12 h; very frequent recurrences (≥ 10/year): 250 mg/12 h.
Prophylaxis of CMV infection and disease in adults and adolescents ≥ 12 years: 2 g/6 h, 90 days.


Hypersensitivity to valacyclovir or acyclovir.

Warnings and Cautions with Valacyclovir

Maintain adequate fluid intake in the elderly and monitor; in renal failure monitor and adjust dose; limited experience in patients with advanced cirrhosis.
Caution in high-dose liver disease (≥ 4 g/day), no specific studies in liver transplantation; concomitant treatment with intravenous antivirals if necessary; risk of: sexual transmission and increased frequency of adverse reactions to high doses in CMV infections.

Liver failure

Limited experience in advanced cirrhosis. Caution in liver disease with high doses (≥ 4 g/day), without specific studies in liver transplantation.

Renal insufficiency

Caution. Adjust dose according to Clcr. Increased risk of adverse neurological effects.

Interactions with Valacyclovir

  • Precaution with: nephrotoxics such as aminoglycosides, organoplatin compounds, iodine contrast media, methotrexate, pentamidine, foscarnet, cyclosporine and tacrolimus (especially if renal failure); drugs that inhibit active renal tubular secretion.
  • Plasma level increased by: cimetidine, probenecid.

Pregnancy and Valacyclovir

Limited data, use only if profit outweighs potential risk.


Acyclovir, the main metabolite of valacyclovir, is excreted in breast milk.
However, therapeutic doses of valacyclovir are not expected to have an effect on newborns or breast-feeding infants as the dose ingested by the child is less than 2% of the therapeutic dose of intravenous acyclovir for the treatment of neonatal herpes.

Valacyclovir should be used with caution during lactation and only when clinically indicated.

Adverse reactions and side effects of Valacyclovir

Headache, nausea; dizziness; vomiting, diarrhea; rashes including photosensitivity, itching.


Source: The content of this active ingredient has been written taking into account the clinical and molecular information of all medicines authorised and marketed in the United States under the Unique Ingredient Identifier (UNII) by the Substance Registration System (SRS) of the Food and Drug Administration (FDA) and the United States Pharmacopeia (USP).

In order to know in detail the information authorized by the FDA for each drug, you should consult the corresponding medication guide authorized by the FDA.


PubChem CID: 60773
NCI Thesaurus: C28235

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