Entecavir Drug Interactions: What to Avoid and What to Tell Your Doctor

Entecavir has a relatively favorable drug interaction profile compared to many other medications—it does not interact with the cytochrome P450 (CYP450) enzyme system, which is responsible for most common drug-drug interactions. However, there are important interactions related to how entecavir is processed by the kidneys, and one critical interaction involving HIV.

How Entecavir Interacts with Other Drugs

Entecavir is primarily eliminated by the kidneys (62–73% of the drug is excreted unchanged in urine). It is processed through both glomerular filtration and active tubular secretion. This is the key to understanding its interactions: any drug that also uses active tubular secretion in the kidneys may compete with entecavir for elimination, raising blood levels of one or both drugs.

Importantly, entecavir is NOT a substrate, inhibitor, or inducer of the CYP450 enzyme system. This means it doesn't interact with most common medications that are metabolized by liver enzymes. This is a significant advantage over many older antivirals.

Critical Interaction: HIV Medications and Undiagnosed HIV

This is entecavir's most important interaction—and it's the subject of an FDA boxed warning. Entecavir has weak anti-HIV activity. If a patient has undiagnosed or untreated HIV infection and takes entecavir alone (without a fully suppressive antiretroviral regimen), the drug may suppress HIV virus just enough to select for drug-resistant HIV mutations, making future HIV treatment harder or even impossible with certain medications.

Action required: Before starting entecavir, every patient should be tested for HIV. If HIV-positive, they must be receiving fully suppressive antiretroviral therapy (HAART) before and throughout entecavir treatment.

Moderate Interactions: Kidney-Excreted Medications

The following drug classes may interact with entecavir by competing for active tubular secretion in the kidneys, potentially raising levels of entecavir or the other drug. Monitor patients closely for adverse effects:

• Tenofovir disoproxil fumarate (TDF): TDF increases entecavir levels by reducing its renal clearance. Use caution when both are prescribed together; monitor for toxicity.
• Elvitegravir/cobicistat/emtricitabine/tenofovir DF (Stribild): Both drugs may increase nephrotoxicity; monitor renal function closely.
• Metformin: Both are secreted by active tubular secretion. Coadministration may increase levels of one or both drugs and could raise the risk of lactic acidosis. Monitor patients with diabetes on metformin closely.
• Aminoglycoside antibiotics (amikacin, tobramycin, gentamicin): Compete for renal tubular secretion; may increase entecavir concentrations and risk of kidney toxicity.
• Cyclosporine and tacrolimus: Immunosuppressants used in organ transplant recipients. Both affect renal function, which can alter entecavir clearance. Studies in liver transplant recipients showed approximately 2-fold higher entecavir exposure. Monitor renal function carefully.
• NSAIDs (ibuprofen, naproxen): Regular use of NSAIDs can reduce kidney function, which may increase entecavir blood levels. Discuss NSAID use with your doctor if you take them regularly.

Interactions That Were Studied and Found NOT Significant

Formal pharmacokinetic studies showed no significant interactions between entecavir and:

• Lamivudine (3TC)
• Adefovir dipivoxil
• Tenofovir disoproxil fumarate (in formal drug-drug interaction studies, though monitoring is still warranted clinically)

Food Interactions: Take on an Empty Stomach

Entecavir itself doesn't interact with specific foods, but food does affect how it's absorbed. Taking entecavir with a standard high-fat meal reduces peak drug levels by up to 44% and overall absorption by 18–20%. This is not an interaction in the traditional sense, but it does mean the drug works less effectively if taken with food.

Always take entecavir on an empty stomach—at least 2 hours after eating and 2 hours before your next meal. Alcohol: while no specific alcohol-entecavir interaction has been documented, alcohol is harmful to the liver, which is already under stress from hepatitis B. Alcohol use should be discussed with your doctor.

What to Tell Your Doctor Before Starting Entecavir

Tell your doctor about all medications, supplements, and herbal products, especially:

• Any HIV medications or history of HIV treatment
• Metformin (Glucophage) or other diabetes medications
• Immunosuppressants (cyclosporine, tacrolimus, sirolimus)
• Any antibiotics, especially aminoglycosides
• Any kidney problems or history of kidney disease
• Regular use of NSAIDs (ibuprofen, naproxen) or diuretics

Also see our guide on entecavir side effects for a full overview of what to watch for. And if you need to find entecavir in stock, medfinder can help you locate it near you.