What are the side effects of Valacyclovir (Valcyclovir)?

From the Guidelines

Valcyclovir is generally well-tolerated with minimal adverse events, and the most common side effects include headache, nausea, and diarrhea, which are usually mild and transient. According to a study published in the Journal of Clinical Virology 1, clinical trials evaluating the safety of valaciclovir for the treatment of herpes labialis have shown that the medication is associated with a low incidence of adverse events. The study found that the number of adverse events and drug-related adverse events was similar in patients treated with valaciclovir and those receiving placebo, with headache being more common in the valaciclovir group. Other adverse events, such as nausea and diarrhea, were also reported, but were generally mild and infrequent.

Some key points to consider when taking valcyclovir include:

• Staying well-hydrated to reduce the risk of kidney-related side effects
• Monitoring for signs of kidney problems, such as decreased urination
• Being aware of the potential for rare but serious side effects, such as severe skin reactions or thrombotic thrombocytopenic purpura (TTP)/hemolytic uremic syndrome (HUS)
• Contacting a healthcare provider immediately if severe side effects occur, especially confusion, hallucinations, or signs of kidney problems.

Overall, the safety profile of valcyclovir is favorable, and the medication can be an effective treatment option for herpes labialis when taken as prescribed 1.

From the FDA Drug Label

To report SUSPECTED ADVERSE REACTIONS, contact GlaxoSmithKline at 1-888-825-5249 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 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. Genital Herpes Initial Episode: 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%) Recurrent Episodes: 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%) Suppressive Therapy: 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%). 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%) Herpes Zoster 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%). Table 2 Incidence (%) of Laboratory Abnormalities in Herpes Zoster and Genital Herpes Trial Populations In addition to adverse events reported from clinical trials, the following events have been identified during postmarketing use of VALTREX. General Facial edema, hypertension, tachycardia. Allergic Acute hypersensitivity reactions including anaphylaxis, angioedema, dyspnea, pruritus, rash, and urticaria Central Nervous System ( CNS) Symptoms Aggressive behavior; agitation; ataxia; coma; confusion; decreased consciousness; dysarthria; encephalopathy; mania; and psychosis, including auditory and visual hallucinations, seizures, tremors

The common side effects of valacyclovir include:

• Headache (reported in 14% to 35% of subjects)
• Nausea (reported in 5% to 11% of subjects)
• Dizziness (reported in 2% to 4% of subjects)
• Abdominal pain (reported in 3% to 11% of subjects)
• Fatigue (reported in 8% of subjects)
• Rash (reported in 8% of subjects) The laboratory abnormalities associated with valacyclovir include:
• Elevated ALT (reported in 1.8% to 14% of subjects)
• Elevated AST (reported in 1% to 16% of subjects)
• Decreased neutrophil counts (reported in 18% of subjects)
• Decreased platelet counts (reported in 3% of subjects) 2

From the Research

Valcyclovir Side Effects

• Valacyclovir is a medication used to treat herpes zoster infection, commonly known as shingles, and can cause severe side effects due to its prolonged half-life in patients with renal dysfunction 3.
• The most common adverse effect of valacyclovir in patients with underlying kidney disease is valacyclovir-associated neurotoxicity (VAN), which can be easily prevented if the medication is properly dosed 3, 4.
• VAN can cause severe neurological and physical manifestations, including confusion, altered level of consciousness, hallucinations, agitation, and dysarthria, and may require hospital admission and emergent hemodialysis 3, 4.
• The risk of neurotoxicity is higher in patients with end-stage renal disease (ESRD) and those with impaired renal function, and the administered dose is often higher than the recommended renal adjustment 3, 4.
• The treatment of valacyclovir-induced neurotoxicity involves discontinuation of the antiviral and, in some cases, additional clearance by dialysis 4.
• Other side effects of valacyclovir include phlebitis, local irritation, and occasionally, reversible renal dysfunction, and dose reduction is recommended in patients with impaired renal function 5, 6.