Furosemide
Lasix
Loop diuretic
Inhibits the Na-K-2Cl cotransporter in the thick ascending loop of Henle. Massive natriuresis + kaliuresis + magnesiuresis. Also a venodilator — drops preload within minutes, before diuresis kicks in.
Indications
- •Acute pulmonary edema / CHF exacerbation
- •Volume overload (CKD, cirrhosis, nephrotic syndrome)
- •Hyperkalemia (adjunct — drives K+ excretion)
- •Reduce intracranial pressure (less common than mannitol; useful when serum osm already high)
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| Acute pulmonary edema | 20–80 mg IV slow push; double dose q1–2 h if no response | 0.5–1 mg/kg IV |
| Maintenance diuresis | 20–40 mg IV/PO q12 h | — |
| Refractory CHF infusion | 5–20 mg/h IV continuous | — |
Pharmacokinetics
IV onset 5 min (venodilation), 30 min (diuresis). Peak 30 min. Duration 2 h. Hepatic + renal elimination. Bioavailability 50% PO — IV typically 2× PO efficacy.
Hemodynamic effects
Acute venodilation drops preload before diuresis (useful in flash pulmonary edema). Sustained diuresis reduces afterload + preload.
Respiratory effects
None directly; resolves pulmonary edema secondarily.
Side effects
- !Hypokalemia (most common reason for arrhythmia post-dose)
- !Hypomagnesemia, hypocalcemia, hyponatremia, hypochloremic metabolic alkalosis
- !Ototoxicity (high IV doses, rapid push, especially with aminoglycosides)
- !Acute renal failure if hypovolemic
- !Sulfa cross-reactivity (rare — most sulfa-allergic patients tolerate it)
Contraindications
- ×Anuria
- ×Severe hypovolemia / dehydration without replacement
- ×Hepatic encephalopathy (drives further alkalosis)
Clinical pearls
- ★SLOW PUSH: > 4 mg/min causes ototoxicity. For > 80 mg, infuse over 30 min.
- ★ELECTROLYTES BEFORE INDUCTION: chronic Lasix patients arrive hypokalemic + alkalotic. Check K+ — < 3.5 with cardiac history = delay or replace before induction.
- ★FUROSEMIDE STRESS TEST: in early AKI, 1–1.5 mg/kg IV; urine output < 200 mL in 2 h predicts progression to severe AKI.
- ★BUMETANIDE EQUIVALENT: 1 mg bumex = 40 mg lasix. Useful when furosemide isn't working — bumetanide has more reliable absorption.
Other drugs in Diuretics
- Mannitol
Freely filtered, not reabsorbed. Pulls water from tissues into vascular space (transient ↑intravascular volume) then drives osmotic diuresis. Reduces ICP by drawing water across an intact blood-brain barrier.
- Acetazolamide
Reversibly inhibits carbonic anhydrase in proximal renal tubule, choroid plexus, ciliary body, RBC. Renal effect: ↓Na/H exchange → bicarbonate diuresis + mild Na/water loss + metabolic acidosis. CNS effect: ↓CSF production. Eye effect: ↓aqueous humor.
- Spironolactone
Competitive antagonist at the mineralocorticoid receptor in the distal nephron → inhibits aldosterone-mediated Na reabsorption + K secretion. Net effect: mild Na/water loss + K retention + Mg retention. Also a weak androgen-receptor antagonist.
- Bumetanide
Inhibits the Na-K-2Cl cotransporter in the thick ascending limb → potent diuresis. ~40× more potent than furosemide (1 mg bumetanide ≈ 40 mg furosemide).
Browse all classes: /reference/drugs
Suggested reading
- •Stoelting & Hines, Pharmacology & Physiology in Anesthetic Practice, 6e
- •Miller's Anesthesia, 9e
- •FDA package insert
