Furosemide Injection and Theophylline: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Furosemide Injection
Theophylline
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
Altered theophylline concentrations
Interaction Deep Dive
Concomitant furosemide and theophylline therapy has been reported to produce increases or decreases in theophylline serum concentrations12. In four premature newborns, concurrent use of theophylline and furosemide resulted in decreased theophylline peak concentration. If agents are administered at least two hours apart, no interactions have been reported to occur 245.
Why it happens (mechanism)
Unknown
Literature reports
1 report — tap to read
a) Administration of a single 40 mg intravenous bolus of furosemide in patients stabilized at steady-state on continuous intravenous aminophylline infusion resulted in an increase (average, 2.9 mcg/mL (16 mcmol/L)) in serum theophylline concentrations (range, 0.5 to 5.5 mcg/mL (3 to 30.5 mcmol/L)). Urine volumes increase by an average of 995 mL above baseline 1. However, one study has suggested that furosemide administration can significantly reduce theophylline serum concentrations in asthmatic patients 2. Contrary to previous reports, 3 reported no significant interaction between theophylline and furosemide in healthy volunteers. Two doses of furosemide 20 mg at 4-hour intervals did not influence steady-state theophylline plasma concentrations. In this study, furosemide induced a moderate diuresis, as well as a reduction in renal clearance, which may explain the lack of effects observed on theophylline serum concentrations.
Common questions
Can I take Furosemide Injection and Theophylline together?
Altered theophylline concentrations Always confirm with your pharmacist or prescriber before making any change.
How serious is the Furosemide Injection and Theophylline interaction?
It is rated minor. Usually limited clinical impact.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Furosemide Injection or Theophylline 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 anything you'd monitor while I'm on both?
References (5)
- Conion PF, Grambau GR, Johnson CE, et al: Effect of intravenous furosemide on serum theophylline concentration. Am J Hosp Pharm 1981; 38:1345-1347. DOI
- Carpentiere C, Marino S, & Castello F: Furosemide and theophylline. Ann Intern Med 1985; 103(6 Part I):957. PubMed
- Janicke AU, Krudewagen B, Schulz A, et al: Absence of a clinically significant interaction between theophylline and furosemide. Eur J Clin Pharmacol 1987; 33:487-491. DOI
- Upton RA: Pharmacokinetic interactions between theophylline and other medication (part I). Clin Pharmacokinet 1991; 20:66-80.
- Toback JW & Gilman ME: Theophylline-furosemide inactivation (letter)?. Pediatrics 1983; 71:140-141. DOI
Keep reading about Furosemide Injection
Keep reading about Theophylline
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