Medical Dictionary Search Engines

Please be patient! It may take up to ONE minute to load all the Engines.
Problems? Please contact our support.


Search For


Specialty Search




WebMD DrugDigest MedicineNet RxList
Other drug names: A-Am An-Az B C-Ch Ci-Cz D-Dh Di-Dz E F G H I-J K-L M-Mh Mi-Mz N-Nh Ni-Nz O P-Pl Pm-Pz Q-R S-Sn So-Sz T-To Tp-Tz U-V W-Z 0-9   

Valacyclovir (Systemic)

Brand Names

In the U.S.-

  • Valtrex

In Canada-

  • Valtrex


  • Antiviral, systemic


Valacyclovir (val-ay-SYE-kloe-veer) is used to treat the symptoms of herpes zoster (also known as shingles), a herpes virus infection of the skin; it is also used to treat and prevent genital herpes infections. In your body, valacyclovir becomes the anti-herpes medicine, acyclovir. Although valacyclovir will not cure shingles or genital herpes, it does help relieve the pain and discomfort and helps the sores heal faster.

Valacyclovir is available only with your doctor's prescription, in the following dosage form:

  • Tablets (U.S. and Canada)

Before Using This Medicine

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For valacyclovir, the following should be considered:

Allergies- Tell your doctor if you have ever had any unusual or allergic reaction to valacyclovir or acyclovir. Also tell your health care professional if you are allergic to any other substances, such as foods, sulfites or other preservatives, or dyes.

Pregnancy- Adequate and well-controlled studies in humans have not been done with valacyclovir or acyclovir. However, acyclovir has been used in pregnant women and has not been reported to cause birth defects or other problems.

Breast-feeding- It is not known whether valacyclovir passes into breast milk. However, acyclovir does pass into breast milk but has not been reported to cause problems in nursing babies.

Children- Studies on this medicine have been done only in adult patients. There is no specific information comparing use of valacyclovir in children with use in other age groups.

Older adults- Valacyclovir has been used in elderly patients and has not been shown to cause different side effects or problems in older people than it does in younger adults. Elderly patients are at a high risk for dehydration and should drink plenty of fluids.

Other medicines- Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change your dose or other precautions may be necessary. Tell your health care professional if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine.

Other medical problems- The presence of other medical problems may affect the use of valacyclovir. Make sure you tell your doctor if you have any other medical problems, especially:
  • Advanced human immunodeficiency virus (HIV) infection or
  • Bone marrow transplantation or
  • Kidney transplantation-Patients with these medical problems may have an increased risk of severe side effects
  • Kidney disease-Kidney disease may increase blood levels of this medicine, increasing the chance of side effects

Proper Use of This Medicine

Valacyclovir works best if it is used within 48 hours after the first symptoms of shingles or genital herpes (for example, pain, burning, or blisters) begin to appear . For recurrent outbreaks of genital herpes, valacyclovir works best if it is used within 24 hours after the symptoms begin to appear.

Valacyclovir may be taken with meals.

Keep taking valacyclovir for the full time of treatment , even if your symptoms begin to clear up after a few days. Do not miss any doses . However, do not use this medicine more often or for a longer time than your doctor ordered .


The dose of valacyclovir will be different for different patients. Follow your doctor's orders or the directions on the label . The following information includes only the average doses of valacyclovir. Your dose may be different if you have kidney disease. If your dose is different, do not change it unless your doctor tells you to do so.

  • For oral dosage form (tablets):
    • For treatment of genital herpes, first outbreak:
      • Adults-1 gram two times a day for ten days.
      • Children-Use and dose must be determined by your doctor.
    • For treatment of genital herpes, recurrent outbreaks:
      • Adults-500 milligrams (mg) two times a day for three days.
      • Children-Use and dose must be determined by your doctor.
    • To prevent recurrent outbreaks of genital herpes:
      • Adults-500 mg or 1 gram once a day.
      • Children-Use and dose must be determined by your doctor.
    • For treatment of shingles:
      • Adults-1 gram three times a day for seven days.
      • Children-Use and dose must be determined by your doctor.

Missed dose-

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.


To store this medicine:

  • Keep out of the reach of children.
  • Store away from heat and direct light.
  • Do not store the tablets in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
  • Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

Precautions While Using This Medicine

If your symptoms do not improve within a few days, or if they become worse, check with your doctor.

The areas affected by genital herpes or shingles should be kept as clean and dry as possible. Also, wear loose-fitting clothing to avoid irritating the sores (blisters).

Side Effects of This Medicine

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do they may need medical attention.

Check with your doctor as soon as possible if the following side effect occurs:

  • Less common
    • Painful menstruation, including abdominal cramps, diarrhea, or nausea 

  • Rare
    • Black, tarry stools;  chest pain;  chills;  cough;  decreased frequency/output of urine;  fever;  flu-like symptoms;  headache;  lower back/side pain;  reduced mental alertness;  shortness of breath;  unusual tiredness;  yellow eyes or skin 

  • Frequency not determined
    • Back, leg or stomach pains;  changes in behavior, especially in interactions with other people;  difficulty breathing or swallowing;  fast, pounding, or irregular heartbeat;  high blood pressure;  itching;  lightheadedness when getting up from a lying or sitting position;  redness of skin ;  seeing, hearing, or feeling things that are not there;  skin rash;  swelling or puffiness of face, hands, legs, or feet;  wheezing  

  • Symptoms of overdose with intravenous acyclovir

    Because the information on valacyclovir overdose is limited, information on intravenous acyclovir overdose is provided. In the body, valacyclovir is converted into acyclovir.

    • Anxiety;  convulsions (seizures);  decrease in urine output;  decreased frequency of urination;  dry mouth;  hallucinations (seeing, hearing, or feeling things that are not there);  irritability;  loss of consciousness ;  lower back/side pain;  nervousness;  restlessness 

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of these side effects continue or are bothersome:

  • More common
    • Headache;  nausea 

  • Less common
    • Constipation;  diarrhea;  dizziness;  joint pain;  loss of appetite;  stomach pain;  unusual tiredness or weakness;  vomiting  

  • Frequency not determined
    • Anxiety;  dry mouth;  irritability;  mood or mental changes;  nervousness;  restlessness 

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.

©2009 [Privacy Policy] [Disclaimer]
Last updated: Tue, 06 Jan 2009 00:20:03 GMT