Can valacyclovir (Valtrex) cause diarrhea?

From the Guidelines

Valacyclovir can cause diarrhea, although it is not a commonly reported adverse event. According to a study published in the Journal of Clinical Virology 1, diarrhea was recorded in patients taking valaciclovir, but the incidence was not significantly higher than in the placebo group. The study found that headache was more common with valaciclovir than with placebo, but other adverse events, such as nausea and diarrhea, were reported in all treatment arms.

Some key points to consider when evaluating the risk of diarrhea with valacyclovir include:

• The incidence of diarrhea was not statistically significant compared to the placebo group 1
• Diarrhea was generally mild and infrequent in patients taking valacyclovir 1
• Other gastrointestinal side effects, such as nausea and abdominal pain, were also reported in patients taking valacyclovir 1
• Staying hydrated and taking the medication with food may help reduce the risk of diarrhea and other gastrointestinal side effects.

It is essential to note that while diarrhea is a possible side effect of valacyclovir, it is not typically severe or persistent. However, if you experience severe, persistent, or bloody diarrhea while taking valacyclovir, you should contact your healthcare provider immediately.

From the FDA Drug Label

Gastrointestinal Diarrhea.

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%),

Valacyclovir can cause diarrhea in some patients, as reported in the clinical trials and postmarketing experience 2, 2.

• The frequency of diarrhea in pediatric subjects aged 1 month to less than 12 years was 5%.
• Diarrhea is also listed as a gastrointestinal adverse reaction in the postmarketing experience section.

From the Research

Valcyclovir and Diarrhea

• Valcyclovir has been associated with diarrhea in some cases, as reported in a study published in 2004 3.
• The study described a case of Clostridium difficile colitis associated with valaciclovir treatment, which led to diarrhea in a 73-year-old man.
• The patient's symptoms worsened over time, and he was eventually diagnosed with C. difficile infection, which was confirmed by a positive stool test.
• Another study published in 2018 found that diarrhea was a common adverse event in patients treated with acyclovir, which is similar to valcyclovir 4.
• However, the study did not find a significant difference in the incidence of diarrhea between patients treated with acyclovir and those treated with famciclovir.

Mechanism of Diarrhea

• The exact mechanism of valcyclovir-induced diarrhea is not fully understood, but it may be related to the disruption of the gut microbiome or the direct effect of the drug on the intestinal mucosa.
• The study published in 2004 suggested that valcyclovir may increase the risk of C. difficile colitis, which can lead to diarrhea 3.
• Another study published in 2008 found that antimotility agents, such as loperamide, can be effective in reducing the duration and severity of diarrhea in patients with traveler's diarrhea 5.

Clinical Implications

• Healthcare professionals should be aware of the potential risk of diarrhea associated with valcyclovir treatment and monitor patients for signs and symptoms of diarrhea.
• Patients who experience diarrhea while taking valcyclovir should be evaluated for underlying causes, such as C. difficile infection, and treated accordingly.
• The use of antimotility agents, such as loperamide, may be considered in patients with diarrhea, but their effectiveness and safety should be carefully evaluated 5.