Tobramycin and Furosemide Injection: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Furosemide Injection
Tobramycin
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Increased tobramycin plasma and tissue concentrations and additive ototoxicity and/or nephrotoxicity
Interaction Deep Dive
Concomitant use of furosemide and tobramycin should be avoided due to potential additive nephrotoxicity and ototoxicity2 except in life-threatening situations 1. Avoid excessive doses of either drug, especially in uremic patients, as there is evidence to suggest that renal dysfunction will increase the risk of ototoxicity 3 Concurrent administration of IV furosemide may increase tobramycin toxicity by altering tobramycin serum and tissue concentrations 2. Coadministration of tobramycin and furosemide may increase risk of ototoxicity, especially in the presence of impaired renal function 1.
Why it happens (mechanism)
Additive or synergistic toxicity
Literature reports
2 reports — tap to read
a) A 70-year-old woman with a history of congestive heart failure was treated with tobramycin following sputum gram stain results indicating gram-negative bacilli. Peak and trough levels following a loading dose of tobramycin 150 mg (2 mg/kg) were 3.7 and 1.5 mcg/mL (7.9 and 3.2 mcmol/L), respectively. The volume of distribution (Vd) was determined to be 0.46 L/kg (normal 0.25 L/kg) and half-life 4.6 hours. The maintenance dose was adjusted to 180 mg IV every 8 hours. The patient received a bolus injection of furosemide 120 mg IV 12 hours after the tobramycin loading dose for extensive edema. Peak and trough levels of tobramycin after the fourth dose were 16.2 and 5.3 mcg/mL (34.7 and 11 mcmol/L; Vd 0.18 L/kg; half-life 4 hours). The authors proposed that the increase in tobramycin serum levels resulted from a decrease in edema (decrease in Vd) since the drug distributes well into extracellular fluid 3.
b) The effects of furosemide-aminoglycoside combination therapy on ototoxicity was studied. As measured by audiograms, toxicity developed in 5 of 23 patients (21.7%) receiving furosemide and aminoglycosides and in 28 of 119 patients (23.5%) who received only an aminoglycoside. However, only a small number of patients received combination therapy, as opposed to single-agent furosemide therapy. Significant differences may have been detected with larger numbers of patients receiving the combination. The same authors also conducted a retrospective study of the influence of furosemide on aminoglycoside-induced nephrotoxicity. Nephrotoxicity was defined as a rise in serum creatinine of greater than or equal to 0.5 mg/dL (40 mcmol/L) if the original concentration was less than 3 mg/dL (300 mcmol/L) or a rise of greater than or equal to 1 mg/dL (90 mcmol/L) if the original concentration was 3 mg/dL (300 mcmol/L) or greater. Results demonstrated nephrotoxicity in 10 of 50 patients (20%) given furosemide and aminoglycoside and in 38 of 222 patients (17.1%) given only an aminoglycoside. The authors concluded that the coadministration of furosemide with aminoglycosides should not be considered a major risk factor for the development of aminoglycoside-induced nephrotoxicity or auditory toxicity 4.
Common questions
Can I take Tobramycin and Furosemide Injection together?
Increased tobramycin plasma and tissue concentrations and additive ototoxicity and/or nephrotoxicity Always confirm with your pharmacist or prescriber before making any change.
How serious is the Tobramycin and Furosemide Injection interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Tobramycin or Furosemide Injection need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (4)
- Product Information: FUROSCIX(R) subcutaneous injection, furosemide subcutaneous injection. scPharmaceuticals Inc (per FDA), Burlington, MA, 2022. DailyMed
- Product Information: TOBI(R) inhalation solution, tobramycin inhalation solution. Cardinal Health, Woodstock, IL, 2007. DailyMed
- Kaka JS, Lyman C, & Kilarski DJ: Tobramycin-furosemide interaction. Drug Intell Clin Pharm 1984; 18:235-238. PubMed
- Smith CR & Lietman PS: Effect of furosemide on aminoglycoside-induced nephrotoxicity and auditory toxicity in humans. Antimicrob Agents Chemother 1983; 23:133-137. DOI
Keep reading about Furosemide Injection
Keep reading about Tobramycin
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
Check another combination
Our instant two-drug interaction checker is almost here.
Still have questions about this combination?
Every question gets a real answer from a licensed pharmacist — free, and usually within a day.
Ask the pharmacist