Valacyclovir (Valtrex) interactions, side effects, and precautions

In this article:

• Valacyclovir drug interactions
• How to minimize valacyclovir interactions
• When to talk to a healthcare provider

In this article

• Valacyclovir drug interactions
• How to minimize valacyclovir interactions
• When to talk to a healthcare provider

Valacyclovir (brand name: Valtrex) is an antiviral drug that’s approved to treat infections caused by the herpes virus, like cold sores, genital herpes, shingles (herpes zoster), and chicken pox. While it can treat a range of herpes infections, it also interacts with certain drugs, alcohol, and pre-existing conditions may affect treatment too. It’s crucial to understand valacyclovir’s possible interactions, since they can worsen side effects and decrease the drug’s effectiveness. Here’s all the information you need. 

Valacyclovir drug interactions

Even though valaclovir’s label says it doesn’t have any significant drug-drug interactions, there are still some medications that can influence how it works or increase the risk of side effects. They include the following:

Antivirals

Valacyclovir and some other antivirals are excreted through the kidneys. Taking both at the same time can overwork the kidneys and sometimes even damage them. At the very least, it can increase the amount of the medications in your bloodstream, increasing the risk of adverse effects and toxicity. 

Typically, these interactions aren’t serious, but they can be, so it’s important to know what to look for. The symptoms of kidney problems include changes in urination, weakness, difficulty breathing, chest pain, nausea, and swelling in the legs, ankles, or feet. If you experience any of these possible side effects, your healthcare provider might change your dosage or try a different drug. 

• Adefovir
• Cidofovir
• Entecavir
• Foscarnet
• Tenofovir

Immunosuppressants

These drugs are commonly prescribed after organ transplants, but they have also been connected to kidney damage. So when combined with another drug that can affect the kidneys, like valacyclovir, it can lead to nephrotoxicity, particularly in people with existing renal impairment. Additionally, an immunosuppressant called mycophenolate mofetil may cause neutropenia—a decrease in a type of white blood cell—when combined with valacyclovir. 

The symptoms of kidney issues from this interaction are similar to those listed above. In contrast, the common symptoms of neutropenia include fever, fatigue, swollen lymph nodes, mouth ulcers, and sore throat. These typically aren’t severe, but definitely warrant a visit to your healthcare provider. 

• Cyclosporine
• Methotrexate
• Tacrolimus
• Mycophenolate mofetil

Aminoglycoside antibiotics

This is yet another drug class that may affect kidney function. When taken simultaneously with valacyclovir, the combined effects on renal function can increase the concentration in the bloodstream and even cause kidney damage.. The symptoms typically aren’t life-threatening, but kidney damage can be serious in the long run, so tell a healthcare provider if you experience any adverse reactions. 

• Amikacin
• Capreomycin
• Paromomycin
• Streptomycin

Other valacyclovir interactions

Other medications might interact with valacyclovir as well. For example, Non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and chemotherapy drugs like axitinib can also potentially contribute to kidney issues, while the H2 blocker cimetidine and the anti-gout medication probenecid can cause elevated levels of valacyclovir in the body. 

Valacyclovir and alcohol

Alcohol can interact with a lot of prescription drugs, and valacyclovir is one of them. Valacyclovir and alcohol consumption can both cause dizziness, drowsiness, nausea, headaches, and upset stomach—so alcohol might exacerbate these side effects. According to Dr. Hannah Kopelman, dermatologist at DermOnDemand, “Alcohol in moderation is usually not an issue, but I caution patients that excessive drinking can contribute to dehydration and impair kidney function, which is important because Valacyclovir relies on proper hydration for safe clearance.”

Additionally, “both alcohol and valacyclovir are metabolized by the liver,” says Dr. Andreas (Andy) Kogelnik, MD, PhD, founder and medical director of ProDx Health. So he recommends avoiding alcohol while taking the drug. 

Valacyclovir and CBD, vitamins, or herbal supplements

There’s no major evidence that valacyclovir interacts with CBD, although cannabis use can cause drowsiness and dizziness, which may worsen valacyclovir’s side effects. And while it hasn’t shown any interactions with vitamins, there isn’t much research on its interactions with herbal products. “Herbal supplements are trickier,” Dr. Kopelman says.”Things like St. John’s Wort or high-dose echinacea can alter immune responses or liver metabolism, so I encourage patients to let me know about any supplements before starting therapy.”

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How to minimize valacyclovir interactions

“The best way to avoid drug interactions is to make sure your prescribing doctor has a complete list of everything you’re taking, including over-the-counter medicines and supplements,” Dr. Kopelman says. 

Dr. Kogelnik adds: “Generally speaking, it’s a medication that you can take with or without food—it is easy on the gut.” But “This is a medication that you definitely want to take with water as the med can drive your kidneys a bit harder than others.”

People with certain medical conditions might be more prone to serious side effects or interactions while taking valacyclovir. “Folks with kidney or immune issues should definitely check in with their provider before going on this class of antivirals,” Dr. Kogelnik says. And people with HIV/AIDS or a weak immune system may not be able to take valacyclovir, since it’s been connected to a serious condition called thrombotic thrombocytopenic purpura / hemolytic uremic syndrome in people with weakened immune systems.

There’s no evidence that it can increase the risk of birth defects or miscarriages, and while it can enter breast milk, there’s no evidence that it can harm newborns. 

When to talk to a healthcare provider about valacyclovir interactions

Mild side effects are common with many drugs, but there are certain circumstances when patients should take action. Per Dr. Kopelman, “patients should see a doctor right away if they develop unusual symptoms like confusion, dizziness, or decreased urine output, since these may point to kidney issues or central nervous system side effects.”

Keep in mind that this article isn’t a complete list of drug interactions, so you should communicate with your health care provider about any medications, supplements, or health problems you have prior to taking valacyclovir.