furosemide
Brand: Lasix
Prototype Drug
Drug Class: loop diuretic
Drug Family: diuretic
Subclass: sulfonamide loop diuretic
Organ Systems: cardiovascularrenal
Mechanism of Action
Inhibits NKCC2 in the thick ascending limb, blocking reabsorption of Na+, K+, and Cl-; increases free water clearance; stimulates prostaglandin release causing renal vasodilation.
Na-K-2Cl cotransporter (NKCC2) in thick ascending limb of loop of Henle
Indications
- acute pulmonary edema
- chronic heart failure
- edema (hepatic, renal, cardiac)
- hypertension
- hypercalcemia
Contraindications
- anuria
- sulfonamide allergy (cross-sensitivity)
- hepatic coma with electrolyte depletion
Adverse Effects
Common
- hypokalemia
- hyponatremia
- hypovolemia
- hypotension
- hypomagnesemia
- metabolic alkalosis
- ototoxicity (high IV doses)
Serious
- ototoxicity (loop diuretic)
- nephrotoxicity (rare)
- severe electrolyte disturbances
Pharmacokinetics (ADME)
| Absorption | 10-100% oral (variable — edematous bowel absorption impaired) |
| Distribution | wide |
| Metabolism | minimal hepatic |
| Excretion | renal 50% unchanged; 50% hepatic glucuronidation |
| Half-life | 2 hours |
| Onset | 30-60 min oral, 5-15 min IV |
| Peak | 1-2 hours |
| Duration | 6-8 hours oral; 2 hours IV |
| Protein Binding | 91-97% |
| Vd | 0.1-0.2 L/kg |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| aminoglycosides | additive ototoxicity; additive nephrotoxicity | major |
| lithium | reduces renal lithium clearance; toxicity risk | major |
| NSAIDs | blunted diuretic response | moderate |
| digoxin | hypokalemia increases digoxin toxicity | major |
Nursing Considerations
- Weigh daily; target 0.5-1 kg/day weight loss in HF decompensation
- Monitor K+, Na+, Mg2+, BUN, creatinine
- Replace K+ when K+ <3.5 mEq/L
- IV dose 2x oral dose in HF (accounting for poor GI absorption)
- Ototoxicity: avoid rapid IV push; max 4 mg/min IV
Clinical Pearls
- Ceiling dose effect: doubling dose above threshold does not increase natriuresis linearly — switch to IV or combination if oral inadequate
- IV bioavailability > oral in acute HF (gut wall edema impairs oral absorption — double the oral dose for IV equivalent)
Safety Profile
Pregnancy use-with-caution
Lactation avoid
Renal Adjustment Required
Hepatic Adjustment Not required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.