Loop diuretics · Cardiovascular
Furosemide
frusemide · Lasix®(brand names vary by market)
The loop diuretic: where congestion goes to drain.
Also: oral liquid, injection, infusion
Mechanism
Inhibits the Na-K-2Cl cotransporter in the thick ascending limb: the kidney's biggest single sodium handle, hence the biggest diuresis.
Indications
- Congestion in heart failure
- Edema in renal and hepatic disease
- Hypertension in advanced CKD
Formulations
Dosing concepts
Threshold drug
Loops have a dose threshold: below it, nothing happens. In renal impairment the threshold rises, so the dose doubles rather than repeats.
Oral vs IV
Oral bioavailability is famously erratic (10-90%); gut edema in decompensation makes IV the reliable route.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~50% (10-90%, erratic)
- Half-life
- ~2 h
- Elimination
- renal: Secreted into the tubule to act from the luminal side; uremic anions compete in CKD
Adverse effects
- Hypokalemia, hypomagnesemiacommon & serious
- Volume depletion, prerenal AKIcommon & serious
- Hyponatremiacommon
- Ototoxicity at high IV doses or with aminoglycosidesserious
- Gout flarescommon
Contraindications & precautions
Contraindications
- Anuria unresponsive to a test dose
- Severe untreated electrolyte depletion
Precautions
- Sulfonamide allergy (usually tolerated, but documented reactions exist)
- Concurrent nephrotoxins
Interactions
- ACE inhibitor / ARB + diuretic + NSAID (the 'triple whammy')avoidAcute kidney injury, classically in a dehydrated older adult who bought ibuprofen for a sore knee.
- Furosemide (high-dose IV) + AminoglycosidescautionOtotoxicity, potentially permanent.
- Loop diuretics + LithiummonitorLithium level drift upward.
Monitoring
Weight (daily in active diuresis)
The most honest congestion meter
Electrolytes and creatinine
Potassium and magnesium fall; creatinine warns of over-diuresis · Within days of any change
Urine output and symptoms
Effectiveness
Counselling points
- Take it in the morning (and early afternoon if twice daily) so the bathroom trips do not own your night.
- Weigh yourself daily in heart failure; a fast gain of 2 kg is a call, not a wait.
Clinical pearls
- Doubling beats repeating: an ineffective loop dose is below threshold, so give more, not again.
References & review
- Furosemide product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-15 · jurisdiction: global · drug information changes; verify against current references before practice use.