What medications cannot be taken with Valtrex?

October 9, 2025 •

4 min read

Over 90 drugs are known to potentially interact with Valtrex (valacyclovir). This makes understanding what medications cannot be taken with Valtrex? an essential conversation to have with your doctor to prevent serious adverse effects, especially on your kidneys.

Quick Summary

Valtrex should not be combined with other drugs that can cause kidney damage, including some NSAIDs, antibiotics, immunosuppressants, and other antivirals. Live vaccines should also be avoided, and doses of Valtrex might need adjustment with certain medications that affect drug levels.

Key Points

Nephrotoxic drugs: Avoid taking Valtrex with medications that can damage the kidneys, such as certain NSAIDs, antibiotics, and chemotherapy drugs, to prevent acute kidney injury.
Immunosuppressants: Be cautious with immunosuppressants like cyclosporine and tacrolimus, as they can combine with Valtrex to cause increased nephrotoxicity.
Live Vaccines: Do not receive live varicella or zoster vaccines while on Valtrex, and adhere to recommended waiting periods to ensure vaccine efficacy.
Renal Clearance: Medications like cimetidine and probenecid can slow the body's clearance of Valtrex, leading to higher drug concentrations and a higher risk of side effects.
Hydration is Key: Maintain adequate hydration, especially if taking higher doses or having a history of kidney issues, to help protect your kidneys.
Compromised Immune Systems: Individuals with advanced HIV/AIDS or organ transplants face an increased risk of severe blood disorders like TTP/HUS when taking Valtrex.
CNS Effects: Higher doses of Valtrex, especially in older adults or those with pre-existing kidney issues, can lead to central nervous system side effects such as confusion and agitation.

Valtrex, the brand name for valacyclovir, is an antiviral medication prescribed to treat viral infections like herpes and shingles. While effective, it's crucial to be aware of potential drug interactions that can increase toxicity and lead to severe complications. Most of the risks are related to its impact on kidney function, since the drug is primarily eliminated by the kidneys.

Nephrotoxic drugs that increase risk

Taking Valtrex with other medications that can be damaging to the kidneys, known as nephrotoxic drugs, significantly increases the risk of acute kidney injury and other renal problems. It is recommended to avoid or use extreme caution with these combinations.

Nonsteroidal Anti-inflammatory Drugs (NSAIDs): Combining NSAIDs such as ibuprofen (Advil, Motrin), naproxen (Aleve), and diclofenac with Valtrex can elevate the risk of kidney damage. One study noted that patients taking both valacyclovir and an NSAID had a significantly higher risk of acute kidney injury compared to those taking acyclovir with an NSAID.
Certain Antibiotics: Some antibiotics are also nephrotoxic and should be used with caution. These include aminoglycosides like gentamicin, amikacin, and tobramycin, as well as vancomycin and bacitracin.
Chemotherapy Drugs: Medications used in chemotherapy, such as cisplatin and methotrexate, can cause kidney issues on their own and should be used with extreme caution alongside Valtrex to avoid compounding the risk.
Other Nephrotoxic Agents: Other drugs like amphotericin B (an antifungal) and lithium can also contribute to kidney strain when combined with Valtrex.

Immunosuppressants and related issues

Patients with compromised immune systems, including those who have had organ transplants or have advanced HIV/AIDS, must be especially careful. The combination of Valtrex with immunosuppressants can lead to heightened nephrotoxicity or other severe blood disorders.

Cyclosporine, Tacrolimus, and Methotrexate: These immunosuppressants, used to prevent organ rejection or treat autoimmune diseases, can increase the risk of kidney damage when taken with Valtrex. For instance, tacrolimus alone can cause kidney problems, and the risk is amplified with Valtrex.
Mycophenolate Mofetil: This immunosuppressant, when combined with Valtrex, may increase the risk of developing neutropenia, a condition characterized by a low white blood cell count.
HIV/AIDS Patients: Patients with advanced HIV/AIDS, kidney transplants, or bone marrow transplants have an increased risk of developing a serious blood disorder called thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) when taking high doses of Valtrex.

Other antivirals and live vaccines

Combining Valtrex with other antiviral agents that also rely on the kidneys for clearance can lead to toxic levels of medication in the bloodstream. Additionally, Valtrex can interfere with the effectiveness of certain vaccines.

Cidofovir and Foscarnet: These antivirals for severe viral infections are also hard on the kidneys. Concomitant use with Valtrex can significantly increase the risk of renal toxicity and should be avoided.
Varicella and Zoster Live Vaccines: Valtrex can interfere with the effectiveness of live, attenuated vaccines against chickenpox (varicella) and shingles (zoster). It is recommended to stop taking Valtrex at least 24 hours before the vaccination and wait at least 14 days after the vaccine before resuming treatment.

Drugs that alter Valtrex levels

Some medications can increase the concentration of Valtrex's active form (acyclovir) in the bloodstream, raising the risk of side effects. This happens because these drugs interfere with the kidneys' ability to clear Valtrex from the body.

Cimetidine: This histamine-2 blocker, used to treat heartburn, can slow the kidneys' clearance of valacyclovir.
Probenecid: An anti-gout medication, probenecid also decreases the renal clearance of valacyclovir, leading to higher levels in the body.

Potential alcohol interaction

While there is no universally known major interaction, healthcare providers often advise against or recommend limiting alcohol consumption while on Valtrex. Both alcohol and Valtrex are metabolized by the liver, and alcohol can exacerbate potential side effects such as headache and drowsiness. Additionally, excessive alcohol consumption can contribute to dehydration, which is a major risk factor for Valtrex-associated kidney problems.

Drug interaction summary table


Drug/Class	Type of Interaction	Risk Level	Details
NSAIDs (e.g., Ibuprofen, Naproxen)	Increased Nephrotoxicity	High	Poses higher risk of acute kidney injury, especially with chronic use.
Immunosuppressants (e.g., Cyclosporine, Tacrolimus)	Increased Nephrotoxicity and Cytopenia	High	Can lead to serious kidney damage or blood count issues (neutropenia).
Antivirals (e.g., Cidofovir, Foscarnet)	Increased Nephrotoxicity	High	Both drugs are cleared by the kidneys, increasing the risk of toxicity and kidney damage.
Live Vaccines (e.g., Varicella, Zoster)	Reduced Vaccine Efficacy	Moderate-High	The antiviral effect of Valtrex can diminish the body's immune response to the live vaccine.
Cimetidine & Probenecid	Elevated Valtrex Levels	Moderate	Can reduce the kidneys' ability to clear Valtrex, potentially increasing side effects.
Alcohol	Exacerbated Side Effects	Moderate	Can worsen dehydration and side effects like dizziness and headache.

Conclusion: Navigating medication interactions

Staying informed about potential drug interactions is critical for anyone taking Valtrex, especially given the risks associated with kidney function. Always inform your healthcare provider of all medications, including over-the-counter drugs, supplements, and vitamins, before starting Valtrex. Maintaining proper hydration is one of the most effective ways to mitigate the risk of kidney problems, particularly if you have pre-existing kidney issues or are elderly. For more details, consult reliable medical resources like the Centers for Disease Control and Prevention's vaccination guidelines.

Frequently Asked Questions

Combining Valtrex with NSAIDs like ibuprofen, naproxen, or diclofenac increases the risk of kidney damage. Your healthcare provider may advise you to avoid this combination or use an alternative, such as acetaminophen, for pain relief.

Combining Valtrex with immunosuppressants like cyclosporine or tacrolimus raises the risk of kidney toxicity. In some cases, like with mycophenolate mofetil, it can also lead to a low white blood cell count (neutropenia).

Yes, Valtrex can reduce the effectiveness of live, attenuated vaccines, such as those for varicella (chickenpox) and zoster (shingles). You should typically stop taking Valtrex for a period before and after receiving such a vaccine, as advised by your doctor.

It is best to limit or avoid alcohol while taking Valtrex. Both can cause side effects like dizziness and headaches. Excessive alcohol consumption can also lead to dehydration, which negatively affects your kidneys and increases the risk of Valtrex toxicity.

Combining Valtrex with other nephrotoxic antiviral medications, like cidofovir or foscarnet, can dangerously increase the risk of kidney damage because they are all processed through the kidneys. This combination should generally be avoided.

Individuals with pre-existing kidney problems, the elderly, and those with compromised immune systems (such as HIV/AIDS patients or transplant recipients) are at a higher risk of experiencing adverse effects and interactions.

Thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) are serious blood disorders that can cause small blood clots, potentially leading to organ damage. There is an increased risk of developing these conditions in immunocompromised patients taking high doses of Valtrex.