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Drug Profile

The information on this site is intended to supplement and enhance, not replace, the advice of a physician who is familiar with your medical history. Decisions about your health should always be made ONLY after detailed conversation with your doctor.

Generic drug name: acyclovir (ay SYE kloe veer)
Brand name(s): SITAVIG, XERESE, ZOVIRAX
GENERIC: not available FAMILY: Drugs for Viral Infection
Find the drug label by searching at DailyMed.

Generic drug name: valacyclovir (val ay SYE kloe veer)
Brand name(s): VALTREX
GENERIC: not available FAMILY: Drugs for Viral Infection
Find the drug label by searching at DailyMed.

Pregnancy and Breast-feeding Warnings [top]

Pregnancy Warning

No valid data are available for these drugs, as they were not tested adequately in animal studies. Use during pregnancy only for clear medical reasons. Tell your doctor if you are pregnant or thinking of becoming pregnant before you take these drugs.

Breast-feeding Warning

Acyclovir is excreted at very high levels in human milk.  Results from a study show that valacyclovir should be administered in a nursing mother with caution and only used when indicated. Because of the potential for serious adverse effects in nursing infants, you should not take these drugs while nursing.

Facts About This Drug [top]

After oral administration, valacyclovir is rapidly broken down to acyclovir in the intestine and liver.[1] Oral acyclovir is approved by the FDA for shingles (herpes zoster), genital herpes, and chicken pox.[2] The ointment form of acyclovir is approved for the initial management of genital herpes and in limited non-life-threatening herpes infection of the mucous membranes in patients with problems with their immune systems.[3] Acyclovir cream is approved by the FDA for cold sores. The...

After oral administration, valacyclovir is rapidly broken down to acyclovir in the intestine and liver.[1] Oral acyclovir is approved by the FDA for shingles (herpes zoster), genital herpes, and chicken pox.[2] The ointment form of acyclovir is approved for the initial management of genital herpes and in limited non-life-threatening herpes infection of the mucous membranes in patients with problems with their immune systems.[3] Acyclovir cream is approved by the FDA for cold sores. The duration of cold sores was reduced on average by only one-half day.[4]

Oral valacyclovir is FDA-approved for shingles, genital herpes, and the treatment of cold sores.[1] The editors of The Medical Letter, a respected independent source of drug information for health professionals, found that valacyclovir only “modestly” shortened the duration of a cold sore by about one day.[5],[1]

Before You Use This Drug [top]

Tell your doctor if you have or have had:

  • pregnancy or are breast-feeding
  • allergies to acyclovir or valacyclovir
  • nerve disease
  • dehydration
  • bone marrow transplant
  • kidney transplant
  • HIV
  • kidney or liver disease

Tell your doctor about any other drugs you take, including aspirin, herbs, vitamins, and other nonprescription products.

When You Use This Drug [top]

  • If you plan to have any surgery, including dental, tell your doctor that you take this drug.
  • Check with your doctor if there is no improvement within a few days.
  • Keep affected areas clean and dry; wear loose clothing.
  • Use of a condom may help to prevent transmission of herpes.

How to Use This Drug [top]

  • If you miss a dose, take it as soon as you remember, but skip it if it is almost time for the next dose. Do not take double doses.
  • Do not share your medication with others.
  • Take the drug at the same time(s) each day.
  • Take with a full glass (eight ounces) of water.
  • Take with or without food.
  • Take this drug for the prescribed length of time. If you stop too soon, your symptoms could come back.
  • For treatment of shingles, herpes simplex, or genital herpes, start drug as soon as possible after symptoms appear.
  • For treatment of chicken pox, start within 24 hours of onset of rash.
  • Store at room temperature with lid on tightly. Do not store in the bathroom. Do not expose to heat, moisture, or strong light. Keep out of reach of children.

Interactions with Other Drugs [top]

Evaluations of Drug Interactions 2003 lists no drugs, biologics (e.g., vaccines, therapeutic antibodies), or foods as causing “highly clinically significant” or “clinically significant” interactions when used together with the drugs in this section. We also found no interactions in the drugs’ FDA-approved professional package inserts. However, as the number of new drugs approved for marketing increases and as more experience is gained with these drugs over time, new interactions may be discovered.

Adverse Effects [top]

Call your doctor immediately if you experience:

  • rash or hives
  • blood in urine
  • confusion or hallucinations
  • trembling
  • abdominal pain
  • lower back pain
  • difficulty breathing
  • decreased frequency or amount of urination
  • nausea or vomiting
  • loss of appetite
  • chills, fever, or sore throat
  • black, tarry stools
  • pinpoint red spots on skin
  • unusual bleeding or bruising
  • chest pain
  • diarrhea
  • unusual thirst
  • seizures
  • unusual tiredness or weakness
  • faintness or lightheadedness
  • swelling of hands, feet, or lower legs
  • changes in vision
  • painful menstruation

Call your doctor if these symptoms continue:

  • diarrhea
  • dizziness
  • headache
  • joint pain
  • nausea or vomiting
  • acne
  • trouble sleeping
  • general feeling of discomfort or illness
  • muscle pain
  • burning, tingling, or prickling sensations
  • mood or mental changes

Signs of overdose:

  • coma
  • nervousness or restlessness
  • lower back or side pain
  • decreased amount of urine
  • decreased frequency of urination
  • hallucinations
  • seizures
  • tremors

If you suspect an overdose, call this number to contact your poison control center: (800) 222-1222.

Periodic Tests[top]

Ask your doctor which of these tests should be done periodically while you are taking this drug:

  • kidney function tests (during long-term, continuous treatment)
  • blood urea nitrogen and creatinine serum tests

last reviewed April 30, 2021