Valtrex 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, Valtrex becomes the anti-herpes medicine, acyclovir. Although Valtrex will not cure shingles or genital herpes, it does help relieve the pain and discomfort and helps the sores heal faster.

Valtrex is available only with your doctor's prescription .

Special precautions

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 Valtrex , the following should be considered:

Allergies— tell your doctor if you have ever had any unusual or allergic reaction to Valtrex 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 Valtrex 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 Valtrex 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 Valtrex in children with use in other age groups.

Older adults— Valtrex 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 Valtrex . 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

Side effects

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

• 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 

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

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.

Keep all appointments with your doctor.

Do not let anyone else take your medication.