Valaciclovir

1 medicine

Valaciclovir is the prodrug of aciclovir, an antiviral for cold sores, genital herpes and shingles that converts to aciclovir in the body. It is cleared by the kidneys, so hydration and dose reduction in kidney impairment matter just as they do for aciclovir.

Valtrex

Valaciclovir

500/1000mg

Valtrex is a antivirals medication containing Valaciclovir, available as 500/1000mg tablets.

from $2.55 / tablet View

Key facts

  • Valaciclovir (sold as Valtrex and generics) is the prodrug of aciclovir: after you swallow it, your body converts it almost completely to aciclovir, giving higher and steadier blood levels from fewer daily doses.
  • It treats cold sores, genital herpes, and shingles (herpes zoster), and can be taken daily to suppress recurrent genital herpes.
  • Like aciclovir, it is cleared by the kidneys. Keep well hydrated and your prescriber must lower the dose if your kidney function is reduced, to avoid crystal formation in the kidneys or confusion and tremor from drug buildup.
  • Seek urgent care for reduced urination, confusion, or fever with unexplained bruising or bleeding.

What valaciclovir treats

Valaciclovir treats infections caused by herpes simplex virus (cold sores, genital herpes) and varicella-zoster virus (shingles). Starting treatment within 72 hours of a shingles rash, or within 24 hours for a genital herpes outbreak, gives the best results. Taken daily at a lower dose, it reduces how often genital herpes recurs and lowers the chance of passing the infection to a partner. It does not cure the underlying viral infection.

How valaciclovir works

Valaciclovir itself is inactive. After absorption from the gut, enzymes in the liver and intestinal wall rapidly convert it to aciclovir, which then enters virus-infected cells. A viral enzyme converts aciclovir to its active triphosphate form, which blocks the viral DNA polymerase and stops the virus copying its DNA. This prodrug design gives roughly three to five times the aciclovir blood levels that oral aciclovir itself achieves, allowing less frequent dosing.

Before you take it

  • Tell your prescriber about any kidney problems, dehydration, or a weakened immune system (for example from HIV, chemotherapy or an organ transplant); these change your dose and monitoring.
  • Drink water regularly during treatment, especially at the higher doses used for shingles.
  • Very high doses used in some immunocompromised or transplant patients have been linked to a rare blood disorder (thrombotic microangiopathy) causing low platelets and kidney injury; report unusual bruising or reduced urination.
  • If you are pregnant or breastfeeding, discuss the risks and benefits with your prescriber first.

Side effects

Common effects are headache, nausea, and abdominal pain.

Stop and seek urgent medical care for any of these:

  • Little or no urine, or swelling of the legs or face.
  • Confusion, agitation, hallucinations, tremor, or unusual drowsiness.
  • Fever with unexplained bruising, bleeding, or extreme tiredness.
  • Signs of an allergic reaction: swelling of the face or throat, or difficulty breathing.

Safety essentials

  • Because valaciclovir converts to aciclovir and is cleared by the kidneys, staying well hydrated and having your dose matched to your kidney function is the single most important safety step, particularly in older adults or anyone with reduced kidney function.
  • People with significantly reduced kidney function are more prone to confusion, agitation, and hallucinations from drug buildup; this usually reverses once the dose is lowered or the drug is stopped.
  • Tell your prescriber about all other medicines, since some, including probenecid, can raise valaciclovir levels further.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.