Valtrex Side Effects

Generic name: valacyclovir

Note: This document contains side effect information about valacyclovir. Some of the dosage forms listed on this page may not apply to the brand name Valtrex.

Some side effects of Valtrex may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

For the Consumer

Applies to valacyclovir: oral tablet

Get emergency medical help if you have any of these signs of an allergic reaction while taking valacyclovir (the active ingredient contained in Valtrex) hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Stop taking valacyclovir and call your doctor right away if you have any of the following signs of a serious side effect that can harm red blood cells:

• fever, easy bruising or bleeding;

• red spots on the skin (not related to herpes or chickenpox);

• bloody diarrhea, vomiting;

• pale or yellowed skin;

• weakness or fainting; or

• urinating less than usual or not at all.

Call your doctor at once if you have any of these other serious side effects:

• pain in your lower back;

• drowsiness, mood changes, increased thirst, loss of appetite, nausea and vomiting;

• swelling, weight gain, feeling short of breath;

• confusion, agitation, aggression, hallucinations, trouble concentrating;

• feeling shaky or unsteady;

• problems with speech or vision; or

• seizure (convulsions).

Less serious side effects of valacyclovir may include:

• nausea, stomach pain;

• headache, dizziness, tired feeling, depression;

• joint pain;

• menstrual pain;

• mild skin rash; or

• stuffy nose, sore throat.

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect.

For Healthcare Professionals

Applies to valacyclovir: oral tablet

Gastrointestinal

Gastrointestinal side effects have included nausea (up to 15%), abdominal pain (up to 11%), and vomiting (up to 6%). Constipation, anorexia, diarrhea, elevated amylase, and elevated serum lipase have been reported. Diarrhea has been reported during postmarketing experience. In clinical trials of otherwise healthy individuals, frequencies were higher for patients over 50 years of age than for younger patients.

Nervous system

Nervous system side effects have included headache (up to 38%) and dizziness (up to 4%). Central nervous system effects including agitation, seizures, and encephalopathy have been reported. Choreiform movements, myoclonus, vasculitic mononeuritis multiplex, somnolence, and Cotard's syndrome have been reported. Agitation, ataxia, coma, decreased consciousness, dysarthria, encephalopathy, seizures, and tremors have been reported during postmarketing experience. Neurotoxicity has been most commonly reported in patients with renal failure, the elderly, and in patients following bone marrow transplant, and is associated with high serum concentrations of acyclovir.

Acyclovir neurotoxicity is almost exclusively seen in patients with renal failure. These patients may have longstanding chronic renal failure, or acute failure which may be attributed to acyclovir. One group of six bone marrow transplant patients exhibited abnormal EEGs with diffuse slowing. Although more commonly seen with intravenous administration of higher doses, neurotoxicity has also been reported in patients receiving oral doses of acyclovir. Following discontinuation of therapy, mental status recovered within about a week. Several patients with chronic renal failure exhibiting neurotoxicity improved dramatically following hemodialysis.

Although there have been no similar reports in clinical trials of valacyclovir completed to date, the assumption may be made that neurotoxicity can also occur with valacyclovir based on the fact that plasma acyclovir concentrations from oral valacyclovir administration tend to be much higher than those obtained with oral acyclovir.

Psychiatric

Psychiatric side effects have included depression (up to 7%) and disorientation. Central nervous system effects including hallucinations, confusion, and delirium have been reported. Aggressive behavior, confusion, mania, and psychosis (including auditory and visual hallucinations) have been reported during postmarketing experience.

Renal

Renal side effects have included acute renal failure, elevated serum creatinine (up to 0.7%), renal toxicity, and renal failure (presenting as an increase in serum creatinine and blood urea nitrogen). Renal failure and renal pain (may be associated with renal failure) have been reported during postmarketing experience. Renal effects are transient and resolve over several days following discontinuation of therapy. Renal damage is most likely due to crystallization of acyclovir in the renal tubules. Patients with preexisting renal insufficiency are at greater risk for developing neurotoxicity and further deterioration in renal function.

Transient renal dysfunction has been reported with both oral and intravenous administration of acyclovir. Crystallization of the drug in the renal tubules is thought to be the mechanism for the development of renal dysfunction based on findings of crystalluria in several case reports and at least one prospective study. Inadequate hydration of the patient and rapid administration of the drug may contribute to the development of crystalluria. Acute tubular necrosis and interstitial nephritis have also been reported in association with acyclovir therapy. Although there have been no similar reports in clinical trials of valacyclovir completed to date, the assumption may be made that renal toxicity can also occur with valacyclovir based on the fact that plasma acyclovir concentrations from oral valacyclovir administration tend to be much higher than those obtained with oral acyclovir.

Hematologic

TTP/HUS, including some fatalities, has been reported during clinical trials in patients with advanced HIV disease and in allogeneic bone marrow transplant and renal transplant recipients, who were receiving 8 g valacyclovir (the active ingredient contained in Valtrex) per day.

Hematologic side effects have included thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS), and decreased neutrophil counts (18%), platelet counts (up to 3%), hemoglobin (up to 0.8%), and white blood cells (up to 1.3%). Thrombocytopenia, aplastic anemia, leukocytoclastic vasculitis, and TTP/HUS have been reported during postmarketing experience.

Hepatic

Hepatic side effects have included elevated AST (up to 16%), ALT (up to 14%), and bilirubin. Liver enzyme abnormalities and hepatitis have been reported during postmarketing experience.

Hypersensitivity

Hypersensitivity side effects have included acute hypersensitivity reactions (including anaphylaxis, angioedema, dyspnea, pruritus, rash, and urticaria) during postmarketing experience. Stevens-Johnson syndrome has been reported.

Dermatologic

Dermatologic side effects have included rash (8%). Erythema multiforme, rashes including photosensitivity, and alopecia have been reported during postmarketing experience.

Cardiovascular

Cardiovascular side effects have included hypertension and tachycardia during postmarketing experience.

Ocular

Ocular side effects have included visual abnormalities during postmarketing experience.

Respiratory

Respiratory side effects have included nasopharyngitis (16%) and upper respiratory tract infection (9%).

Musculoskeletal

Musculoskeletal side effects have included arthralgia (up to 6%).

Genitourinary

Genitourinary side effects have included dysmenorrhea (up to 8%).

Other

Other side effects have included fatigue (8%). Facial edema has been reported during postmarketing experience.

Metabolic

Metabolic side effects have included elevated alkaline phosphatase (4%) and hypoglycemia. At least one case of hypercalcemia has been reported.

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