diuretic

Furosemide

Lasix

Route: IV · IM · oral
Onset: 5 minutes (IV); 30–60 minutes (oral)
Duration: 2–4 hours (IV); 6–8 hours (oral)

Mechanism of action

Loop diuretic. Inhibits Na+/K+/2Cl− cotransporter (NKCC2) in the thick ascending limb of Loop of Henle → blocks reabsorption of Na+, K+, and Cl− → profound diuresis. Also reduces preload via venodilation (acute effect).

Dosing

Adult: Oral: 20–80 mg/day. IV: 20–80 mg bolus; may double q2h to max 200 mg single dose. Continuous infusion: 0.05–0.5 mg/kg/hr after loading dose
Pediatric: 1–2 mg/kg IV q6–12h; max 6 mg/kg/day
Neonatal: 1–2 mg/kg IV q12–24h; use with caution (nephrocalcinosis risk)

Indications

Pulmonary edema (acute — cardiogenic)
CHF with fluid overload
Hypertension
Nephrotic syndrome / cirrhosis with ascites
Hypercalcemia (with saline)
Fluid overload in mechanically ventilated patients

Contraindications

Anuria (no urine production — obstruction must be ruled out)
Hypovolemia/dehydration
Electrolyte depletion (severe hypokalemia)
Allergy to sulfonamides (cross-reactivity risk — low but documented)

Side effects

Hypokalemia (most common and clinically important)
Hyponatremia
Hypomagnesemia
Hypochloremic metabolic alkalosis
Ototoxicity (high doses IV — esp. with aminoglycosides)
Hyperuricemia / gout
Dehydration and hypovolemia
Azotemia (pre-renal)

Monitoring parameters

Serum electrolytes (K+, Na+, Mg2+, Cl−) — before and after doses
BUN and creatinine (pre-renal azotemia)
Urine output
Blood pressure
Daily weights
Hearing (prolonged high-dose IV use)

Drug interactions

Aminoglycosides (additive ototoxicity — significant)
Digoxin (hypokalemia increases toxicity — monitor K+)
NSAIDs (reduce diuretic effect)
Lithium (furosemide increases lithium levels)
Probenecid (reduces furosemide effect)

NBRC high-yield

Loop diuretic — inhibits NKCC2 in Loop of Henle
Most common side effect: hypokalemia
Monitor K+, Na+, Mg2+, BUN/Cr with use
Ototoxicity: rapid IV infusion or combination with aminoglycosides
Digoxin toxicity potentiated by hypokalemia
IV onset: 5 minutes (venodilation before diuresis)

Clinical pearls

IV Lasix has immediate venodilatory effect before diuresis begins — reduces preload quickly
Administer IV no faster than 4 mg/min (ototoxicity risk at rapid infusion rates)
Replete potassium and magnesium with aggressive diuresis
Hypokalemia + digoxin = dangerous combination — monitor closely
In renal failure: higher doses needed (GFR-dependent efficacy)
Furosemide in neonates: risk of nephrocalcinosis with chronic use

Mnemonic

LASIX: Lose A Salt In eXcess — K, Na, Mg, Cl all lost with the urine

All Drugs

Clinical pearls

IV Lasix has immediate venodilatory effect before diuresis begins — reduces preload quickly

Administer IV no faster than 4 mg/min (ototoxicity risk at rapid infusion rates)

Replete potassium and magnesium with aggressive diuresis

Hypokalemia + digoxin = dangerous combination — monitor closely

In renal failure: higher doses needed (GFR-dependent efficacy)

Furosemide in neonates: risk of nephrocalcinosis with chronic use