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What is Valtrex (valacyclovir)?
Valtrex (valacyclovir) is a type of antiviral drug called a nucleoside analog which is active against the herpes viruses. It is used to treat infections with shingles (herpes zoster), genital herpes (herpes simplex genitalis), and cold sores (herpes labialis).
Valtrex stops the spread of herpes virus in the body by preventing the replication of viral DNA that is necessary for viruses to multiply. Valtrex is actually a “prodrug,” in that it is not active itself. Rather, it is converted to acyclovir in the body, and it is the acyclovir that is active against the viruses. (Acyclovir itself is available as a topical, oral and intravenous medication.)
Valtrex, therefore, is active against the same viruses as acyclovir, but Valtrex has a longer duration of action than acyclovir, and, therefore, can be taken fewer times each day.
Common side effects of Valtrex include:
- abdominal pain,
- cold symptoms,
- increased liver enzymes,
- reduction of white blood cells,
- joint pain, and
Serious side effects of Valtrex include:
- increased heart rate,
- encephalopathy (a disorder of the brain),
- decreased number of blood platelets,
- increased heart rate, and
- high blood pressure (hypertension).
Drug interactions of Valtrex include:
- probenecid and cimetidine, which may reduce the kidney's clearance of Valtrex, leading to higher concentrations in the blood. This may lead to side effects of Valtrex.
There has been no adequate evaluation of Valtrex in pregnant women. The incidence of birth defects in women taking acyclovir is about the same as in the general population. Valtrex should only be used during pregnancy when the benefits to the mother outweigh risks to the fetus.
It is unknown if Valtrex is excreted into breast milk. Among women taking acyclovir, concentrations of acyclovir in breast milk are about four times higher than in the mother's blood. The safety of Valtrex in breastfeeding infants has not been established. Methods other than breastfeeding should be considered if Valtrex must be taken while nursing.
What are the important side effects of Valtrex (valacyclovir)?
The side effect profile of Valtrex is similar to that of acyclovir (Zovirax).
Common side effects are:
- Abdominal pain
- Cold symptoms
- Increased liver enzymes
- Reduction of white blood cells
Other important side effects are:
More serious side effects include central nervous system side effects which are more likely to happen in the elderly, for example:
Valtrex (valacyclovir) side effects list for healthcare professionals
The following serious adverse reactions are discussed in greater detail in other sections of the labeling:
- Thrombotic Thrombocytopenic Purpura/Hemolytic Uremic Syndrome.
- Acute Renal Failure.
- Central Nervous System Effects.
The most common adverse reactions reported in at least 1 indication by greater than 10% of adult subjects treated with Valtrex and observed more frequently with Valtrex compared with placebo are headache, nausea, and abdominal pain. The only adverse reaction reported in greater than 10% of pediatric subjects aged less than 18 years was headache.
Clinical Trials Experience In Adult Subjects
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in practice.
Cold Sores (Herpes Labialis)
In clinical trials for the treatment of cold sores, the adverse reactions reported by subjects receiving Valtrex 2 grams twice daily (n = 609) or placebo (n = 609) for 1 day, respectively, included headache (14%, 10%) and dizziness (2%, 1%). The frequencies of abnormal ALT (greater than 2 x ULN) were 1.8% for subjects receiving Valtrex compared with 0.8% for placebo. Other laboratory abnormalities (hemoglobin, white blood cells, alkaline phosphatase, and serum creatinine) occurred with similar frequencies in the 2 groups.
In a clinical trial for the treatment of initial episodes of genital herpes, the adverse reactions reported by greater than or equal to 5% of subjects receiving Valtrex 1 gram twice daily for 10 days (n = 318) or oral acyclovir 200 mg 5 times daily for 10 days (n = 318), respectively, included headache (13%, 10%) and nausea (6%, 6%). For the incidence of laboratory abnormalities see Table 2.
In 3 clinical trials for the episodic treatment of recurrent genital herpes, the adverse reactions reported by greater than or equal to 5% of subjects receiving Valtrex 500 mg twice daily for 3 days (n = 402), Valtrex 500 mg twice daily for 5 days (n = 1,136), or placebo (n = 259), respectively, included headache (16%, 11%, 14%) and nausea (5%, 4%, 5%). For the incidence of laboratory abnormalities see Table 2.
Suppression of Recurrent Genital Herpes in Immunocompetent Adults
In a clinical trial for the suppression of recurrent genital herpes infections, the adverse reactions reported by subjects receiving Valtrex 1 gram once daily (n = 269), Valtrex 500 mg once daily (n = 266), or placebo (n = 134), respectively, included headache (35%, 38%, 34%), nausea (11%, 11%, 8%), abdominal pain (11%, 9%, 6%), dysmenorrhea (8%, 5%, 4%), depression (7%, 5%, 5%), arthralgia (6%, 5%, 4%), vomiting (3%, 3%, 2%), and dizziness (4%, 2%, 1%). For the incidence of laboratory abnormalities see Table 2.
Suppression of Recurrent Genital Herpes in HIV-1−Infected Subjects
In HIV-1−infected subjects, frequently reported adverse reactions for Valtrex (500 mg twice daily; n = 194, median days on therapy = 172) and placebo (n = 99, median days on therapy = 59), respectively, included headache (13%, 8%), fatigue (8%, 5%), and rash (8%, 1%). Post-randomization laboratory abnormalities that were reported more frequently in valacyclovir subjects versus placebo included elevated alkaline phosphatase (4%, 2%), elevated ALT (14%, 10%), elevated AST (16%, 11%), decreased neutrophil counts (18%, 10%), and decreased platelet counts (3%, 0%), respectively.
Reduction of Transmission
In a clinical trial for the reduction of transmission of genital herpes, the adverse reactions reported by subjects receiving Valtrex 500 mg once daily (n = 743) or placebo once daily (n = 741), respectively, included headache (29%, 26%), nasopharyngitis (16%, 15%), and upper respiratory tract infection (9%, 10%).
In 2 clinical trials for the treatment of herpes zoster, the adverse reactions reported by subjects receiving Valtrex 1 gram 3 times daily for 7 to 14 days (n = 967) or placebo (n = 195), respectively, included nausea (15%, 8%), headache (14%, 12%), vomiting (6%, 3%), dizziness (3%, 2%), and abdominal pain (3%, 2%). For the incidence of laboratory abnormalities see Table 2.
Table 2. Incidence (%) of Laboratory Abnormalities in Herpes Zoster and Genital Herpes Trial Populations
|Laboratory Abnormality||Herpes Zoster||Genital Herpes Treatment||Genital Herpes Suppression|
|Valtrex 1 gram 3 Times Daily|
(n = 967)
(n = 195)
|Valtrex 1 gram Twice Daily|
(n = 1,194)
|Valtrex 500 mg Twice Daily|
(n = 1,159)
(n = 439)
|Valtrex 1 gram Once Daily|
(n = 269)
|Valtrex 500 mg Once Daily|
(n = 266)
(n = 134)
(<0.8 x LLN)
|White blood cells|
(<0.75 x LLN)
(>2 x ULN)
(>1.5 x ULN)
|a Data were not collected prospectively.|
LLN = Lower limit of normal.
ULN = Upper limit of normal.
Clinical Trials Experience In Pediatric Subjects
The safety profile of Valtrex has been studied in 177 pediatric subjects aged 1 month to less than 18 years. Sixty-five of these pediatric subjects, aged 12 to less than 18 years, received oral tablets for 1 to 2 days for treatment of cold sores. The remaining 112 pediatric subjects, aged 1 month to less than 12 years, participated in 3 pharmacokinetic and safety trials and received valacyclovir oral suspension. Fifty-one of these 112 pediatric subjects received oral suspension for 3 to 6 days. The frequency, intensity, and nature of clinical adverse reactions and laboratory abnormalities were similar to those seen in adults.
Pediatric Subjects Aged 12 To Less Than 18 Years (Cold Sores)
In clinical trials for the treatment of cold sores, the adverse reactions reported by adolescent subjects receiving Valtrex 2 grams twice daily for 1 day, or Valtrex 2 grams twice daily for 1 day followed by 1 gram twice daily for 1 day (n = 65, across both dosing groups), or placebo (n = 30), respectively, included headache (17%, 3%) and nausea (8%, 0%).
Pediatric Subjects Aged 1 Month To Less Than 12 Years
Adverse events reported in more than 1 subject across the 3 pharmacokinetic and safety trials in children aged 1 month to less than 12 years were diarrhea (5%), pyrexia (4%), dehydration (2%), herpes simplex (2%), and rhinorrhea (2%). No clinically meaningful changes in laboratory values were observed.
In addition to adverse events reported from clinical trials, the following events have been identified during postmarketing use of Valtrex. Because they are reported voluntarily from a population of unknown size, estimates of frequency cannot be made. These events have been chosen for inclusion due to a combination of their seriousness, frequency of reporting, or potential causal connection to Valtrex.
Central Nervous System (CNS) Symptoms
Hepatobiliary Tract And Pancreas
Liver enzyme abnormalities, hepatitis.
Renal failure, renal pain (may be associated with renal failure).
Valtrex (valacyclovir) is a type of antiviral drug called a nucleoside analog which is active against the herpes viruses. It is used to treat infections with shingles (herpes zoster), genital herpes (herpes simplex genitalis), and cold sores (herpes labialis). Common side effects of Valtrex include headache, nausea, vomiting, abdominal pain, cold symptoms, increased liver enzymes, reduction of white blood cells, diarrhea, rash, joint pain, and dizziness. There has been no adequate evaluation of Valtrex in pregnant women. It is unknown if Valtrex is excreted into breast milk.
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Related Disease Conditions
Cold Sores (Nongenital Herpes Simplex Infections)
Herpes simplex infections are common and when they appear around the mouth and lips, people often refer to them as "cold sores" and "fever blisters." Canker sores are different than cold sores. Air droplets can spread the virus, as can direct contact with the fluid from the blisters. Cold sore treatment include over-the-counter medication, as well as prescription medications.
Shingles, or herpes zoster, is a painful rash caused by the varicella zoster virus. Other shingles symptoms include headache, fever, nausea, and body aches. Treatment focuses on pain management and shortening the duration of the illness with antiviral medications.
Genital Herpes in Women (Symptoms, Signs, Treatment)
Genital herpes is a sexually transmitted disease (STD) caused by the herpes simplex virus (HSV). Symptoms of genital herpes include painful blisters and often fever, body aches, and swollen lymph nodes for first time infection. Genital herpes is diagnosed with lab tests to test for the presence of the virus. Treatment for genital herpes includes antiviral medications to shorten the duration of the outbreak or reduce the risk of future outbreaks. There is no cure for genital herpes. Condoms may help prevent the spread of genital herpes.
Herpes Viral Infections of the Eye
Herpes of the eye occurs due to herpes simplex virus-1 (HSV-1). Symptoms of herpes of the eye include pain in and around the eye, rash or sores on the eyelids, redness, swelling, and cloudiness of the cornea.
Treatment & Diagnosis
Medications & Supplements
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
Professional side effects and drug interactions sections courtesy of the U.S. Food and Drug Administration.