Furosemide
Brand names: Lasix
Class: 💦 Diuretics
The NP-board angle on furosemide is matching it to volume overload — not to chronic hypertension. It blocks the Na-K-2Cl cotransporter in the thick ascending loop of Henle, producing rapid natriuresis and diuresis useful in acute pulmonary edema, decompensated heart failure, ascites with diuretic resistance, and AKI/CKD volume overload. The electrolyte signature is opposite the thiazide on calcium: low potassium, low magnesium, low calcium. Other harms include ototoxicity (worse with rapid IV push and aminoglycoside co-use), hyperuricemia, and dehydration. Bioavailability is variable — IV-to-PO ratio is roughly 1:2 for furosemide. Torsemide and bumetanide have more reliable absorption when oral furosemide stops working in advanced HF.
✅ Indications
CHF/pulmonary edema, ascites, severe HTN, AKI/CKD fluid overload.
⚙️ Mechanism of Action
Loop diuretic — Na-K-2Cl symporter in thick ascending limb.
📏 Dosing
IV: 20–40 mg bolus. PO: 20–80 mg daily or BID. IV:PO ratio = 1:2.
🚫 Contraindications
Anuria, severe dehydration.
⚠️ Adverse Effects
Hypokalemia, hypomagnesemia, hyponatremia, HYPOcalcemia, hyperuricemia, ototoxicity (rapid IV high-dose), metabolic alkalosis.
🔬 Monitoring
BMP, magnesium, daily weights in CHF, urine output.
💎 Board Pearls
- 👂 OTOTOXICITY with rapid IV push at high doses → infuse slowly.
- ⚖️ PO:IV = 2:1 ratio. 40 mg PO ≈ 20 mg IV.
- 🧮 Loop diuretic ↓Ca²⁺ (vs thiazide which ↑Ca²⁺) — the classic calcium differentiator.
Practice Questions
A 76-year-old man in acute decompensated heart failure with pulmonary edema receives a rapid intravenous push of furosemide (Lasix) 120 mg. Within 20 minutes he reports a high-pitched ringing in both ears and new difficulty hearing the nurse. Which mechanism best explains these new symptoms?
Related Drugs in This Class
- Hydrochlorothiazide — HCTZ, Microzide
- Chlorthalidone — Hygroton, Thalitone
- Spironolactone — Aldactone
Sources
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