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

Furosemide (Lasix) has interactions with over 300 medications. Most are minor, but some are clinically significant and can cause serious harm. Because furosemide affects your kidneys, electrolytes, and blood pressure, it can interact with many drugs in unexpected ways. Here's what every patient on furosemide needs to know.

High-Risk Interactions: Avoid or Use with Extreme Caution

Aminoglycoside Antibiotics (gentamicin, neomycin, amikacin, tobramycin)

Risk: Severe ototoxicity (hearing loss) and nephrotoxicity (kidney damage). Both furosemide and aminoglycoside antibiotics can independently cause hearing damage and kidney injury. When combined, the risk of both effects multiplies. This combination should be avoided whenever possible, or used with extreme caution with close monitoring if there is no alternative.

Ethacrynic Acid (Edecrin)

Risk: Contraindicated — greatly increased ototoxicity risk. Using furosemide and ethacrynic acid together is contraindicated. The risk of irreversible hearing loss is extremely high with this combination.

Cisplatin (Cancer Drug)

Risk: Increased kidney damage and hearing loss. Cisplatin is a chemotherapy drug that is already nephrotoxic and ototoxic. Furosemide amplifies these risks. Cancer patients receiving cisplatin who also need diuretics require careful management.

Moderate-Risk Interactions: Use with Caution and Monitoring

NSAIDs (Ibuprofen, Naproxen, Indomethacin, Aspirin)

Risk: Reduced effectiveness of furosemide; potential kidney problems. NSAIDs inhibit prostaglandin synthesis, which furosemide relies on to produce its diuretic effect. This can significantly reduce furosemide's effectiveness at removing fluid. High-dose aspirin and other salicylates also interact. Patients on furosemide should minimize NSAID use and discuss with their doctor before taking any OTC pain relievers.

Lithium

Risk: Elevated lithium blood levels, increased lithium toxicity. By causing sodium loss, furosemide prompts the kidneys to retain lithium instead. This raises lithium levels in the blood and can cause lithium toxicity (confusion, tremors, nausea, seizures). Lithium levels must be monitored closely when adding or changing furosemide doses.

Digoxin (Lanoxin)

Risk: Increased digoxin toxicity via hypokalemia. Furosemide causes potassium loss, and low potassium makes digoxin much more toxic—increasing the risk of life-threatening heart arrhythmias. Patients on both drugs need frequent potassium monitoring and may need potassium supplements.

ACE Inhibitors and ARBs (lisinopril, enalapril, losartan, valsartan)

Risk: Excessive blood pressure drop (hypotension) and potential kidney problems. Both furosemide and ACE inhibitors/ARBs lower blood pressure, and the combination can cause an excessive drop—especially on the first dose. When adding furosemide to an ACE inhibitor regimen, the dose of other antihypertensives may need to be reduced by 50%.

Methotrexate

Risk: Increased methotrexate levels and toxicity. Both drugs compete for tubular secretion in the kidneys. Furosemide can reduce methotrexate elimination, raising blood levels and the risk of methotrexate toxicity (nausea, mucositis, bone marrow suppression).

Cyclosporine (Sandimmune)

Risk: Increased risk of gouty arthritis. Both furosemide and cyclosporine can raise uric acid levels. Together they significantly increase the risk of triggering a gout attack.

Phenytoin (Dilantin)

Risk: Reduced furosemide absorption and effectiveness. Phenytoin interferes with furosemide's absorption from the gut and also interferes with its action in the kidneys. Patients on phenytoin may need higher furosemide doses to achieve the same effect.

Sucralfate (Carafate)

Risk: Reduced furosemide absorption. Sucralfate binds to furosemide in the gut and prevents it from being absorbed. Always take furosemide at least 2 hours before or 2 hours after sucralfate.

What About Food and Alcohol Interactions?

Alcohol: Alcohol can add to the blood pressure-lowering and dizziness effects of furosemide. Moderation is advised.

Potassium-rich foods: Recommended to help offset furosemide's potassium-lowering effect. Bananas, oranges, spinach, potatoes, and avocado are all good sources.

Licorice root (herbal supplement): Can cause additional potassium loss. Avoid when taking furosemide.

What to Tell Your Doctor and Pharmacist

Before starting furosemide, give your healthcare team a complete list of all medications, including:

All prescription medications

Over-the-counter medications (especially NSAIDs like ibuprofen and naproxen)

Vitamins and mineral supplements (including potassium supplements)

Herbal supplements

See also: Furosemide side effects: what to expect and when to call your doctor.

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