Does Valtrex (valacyclovir) interact with diltiazem?

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Valtrex and Diltiazem Drug Interaction

Valtrex (valacyclovir) does not have any clinically significant drug interactions with diltiazem, and these medications can be safely administered together without dosage adjustments or additional monitoring.

Mechanism of Action and Metabolism

Valtrex (valacyclovir) and diltiazem have different metabolic pathways, which explains their lack of significant interaction:

  • Valtrex (valacyclovir): A prodrug of acyclovir that is primarily eliminated through renal excretion
  • Diltiazem: Metabolized primarily through the CYP3A4 enzyme system

Evidence Supporting No Significant Interaction

The available guidelines do not list Valtrex (valacyclovir) among medications that interact with diltiazem. When examining the comprehensive drug interaction tables from multiple cardiovascular and hepatology guidelines, there is no mention of an interaction between these two medications:

  • The American College of Cardiology/American Heart Association guidelines list numerous medications that interact with diltiazem, but Valtrex is not among them 1
  • The European Association for the Study of the Liver (EASL) guidelines provide extensive tables of drug interactions with cardiovascular medications including diltiazem, but do not mention Valtrex or valacyclovir 1

Diltiazem's Known Drug Interactions

Diltiazem is known to interact with several medications because it:

  1. Is a moderate inhibitor of CYP3A4 enzyme 1
  2. Is a P-glycoprotein (P-gp) inhibitor 1

Medications that do have significant interactions with diltiazem include:

  • Ivabradine
  • Ticagrelor
  • Apixaban
  • Cyclosporine
  • Everolimus
  • Simvastatin
  • Ranolazine
  • Various other CYP3A4 substrates 1

Clinical Implications

When prescribing diltiazem with Valtrex:

  • No dosage adjustments are required for either medication
  • No additional monitoring is necessary specifically for this combination
  • Standard monitoring for each medication's individual effects should continue

Potential Considerations

While no direct interaction exists between Valtrex and diltiazem, clinicians should be aware that:

  • Both medications may require dose adjustments in patients with renal impairment, but this is due to their individual pharmacokinetics, not an interaction between them
  • Monitoring for the individual side effects of each medication remains important

Conclusion

The absence of Valtrex from all drug interaction tables with diltiazem in major cardiovascular and hepatology guidelines strongly supports that there is no clinically significant interaction between these medications. They can be safely administered concurrently without special precautions beyond the standard monitoring recommended for each medication individually.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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