Can Valtrex (valacyclovir) cause fatigue?

Can Valtrex Cause Fatigue?

Yes, Valtrex (valacyclovir) can cause fatigue, as fatigue is listed as a side effect in HIV-infected patients taking the medication according to the FDA drug label. 1

Evidence from FDA Drug Label

The FDA-approved drug label for Valtrex specifically mentions fatigue as an adverse reaction:

• In HIV-1-infected subjects, frequently reported adverse reactions for Valtrex (500 mg twice daily) included fatigue (8% vs. 5% with placebo) 1
• While fatigue is not listed among the most common adverse reactions in immunocompetent adults, it is specifically noted in the HIV population

Frequency and Severity of Fatigue

The fatigue associated with Valtrex appears to be:

• Relatively common (8% of HIV patients)
• Generally mild to moderate in severity
• Not typically listed as a reason for discontinuation in clinical trials
• More common than with placebo (8% vs. 5%) 1

Other Common Side Effects

For context, the most common adverse reactions reported in at least one indication by greater than 10% of adult subjects treated with Valtrex include:

• Headache
• Nausea
• Abdominal pain 1

Mechanism of Fatigue

While the exact mechanism by which Valtrex may cause fatigue is not explicitly stated in the evidence, it's important to note that:

• Valtrex is a prodrug of acyclovir
• It works by inhibiting viral DNA synthesis
• Fatigue may be related to the drug's effects on cellular metabolism or immune function

Risk Factors for Developing Fatigue

Patients who may be at higher risk for experiencing fatigue with Valtrex include:

• HIV-infected individuals 1
• Those with renal impairment (as drug clearance is reduced)
• Elderly patients
• Patients taking multiple medications

Management of Valtrex-Associated Fatigue

If a patient experiences fatigue while taking Valtrex, consider:

1. Evaluating for other causes of fatigue (anemia, thyroid dysfunction, depression)
2. Assessing the severity and impact on quality of life
3. Ensuring adequate hydration and nutrition
4. Implementing energy conservation techniques
5. Discussing with the prescriber about:
   • Continuing the medication if the fatigue is mild and the antiviral benefit outweighs the side effect
   • Dose adjustment if appropriate
   • Alternative antiviral medications if fatigue is severe

Clinical Perspective

It's worth noting that some research has explored using antiviral medications including valacyclovir for treating chronic fatigue syndrome in specific patient populations with suspected viral triggers 2, 3, 4. In these contexts, valacyclovir has been studied as a potential treatment for fatigue rather than a cause of it, particularly in patients with elevated antibody titers against certain herpesviruses.

Important Precautions

Be aware of more serious adverse effects that require immediate medical attention:

• Thrombotic Thrombocytopenic Purpura/Hemolytic Uremic Syndrome
• Acute Renal Failure
• Central Nervous System Effects 1

In rare cases, valacyclovir can cause serious neurological adverse effects including hallucinations, confusion, and seizures, particularly in patients with renal impairment 5.