FUROSEMIDE
Clinical safety rating: safe
Other ototoxic drugs may increase risk of hearing loss NSAIDs may reduce the diuretic effect Profound diuresis and electrolyte depletion can occur.
Furosemide is a loop diuretic that inhibits the Na-K-2Cl cotransporter in the thick ascending limb of the loop of Henle, reducing reabsorption of sodium, chloride, and potassium ions, leading to increased urine output.
| Metabolism | Furosemide is primarily metabolized via glucuronidation (by UGT1A1, UGT1A9) and to a lesser extent by CYP450 enzymes (minor). |
| Excretion | Renal (50-80% unchanged; remainder as glucuronide metabolite); fecal (<2%). |
| Half-life | 0.5-2 hours (terminal); prolonged in renal impairment (up to 9-24 hours) and hepatic cirrhosis (up to 2-4 hours). |
| Protein binding | 91-99% (primarily to albumin). |
| Volume of Distribution | 0.1-0.2 L/kg; increased in neonates (0.2-0.4 L/kg) and disease states (e.g., heart failure, cirrhosis). |
| Bioavailability | Oral: 50-60% (variable, 10-100% range due to food and formulation); IM: 100% (relative to IV). |
| Onset of Action | IV: 5 min; IM: 30 min; Oral: 30-60 min. |
| Duration of Action | IV: 2 hours; Oral: 6-8 hours. Diuresis may persist longer in renal impairment. |
| Molecular Weight | 330.75 |
Adults: 20-80 mg orally once or twice daily; IV/IM: 20-40 mg once or twice daily, may increase by 20-40 mg every 6-8 hours. Max dose: 600 mg/day.
| Dosage form | INJECTABLE |
| Renal impairment | GFR 10-50 mL/min: dose unchanged; GFR <10 mL/min: avoid use or use with caution; anuric patients: contraindicated. |
| Liver impairment | Child-Pugh A-B: no adjustment; Child-Pugh C: reduce dose by 50% and monitor response; increased risk of hypokalemia and volume depletion. |
| Pediatric use | Oral: 1-2 mg/kg/dose every 6-12 hours; IV/IM: 1 mg/kg/dose every 6-12 hours; max dose: 6 mg/kg/dose. Not recommended in neonates unless critical. |
| Geriatric use | Start at lowest effective dose (e.g., 20 mg orally once daily); monitor electrolytes, renal function, and volume status closely; avoid excessive diuresis. |
| 1st trimester | Avoid unless clearly indicated; may cause oligohydramnios due to decreased fetal renal perfusion. |
| 2nd trimester | Use only if potential benefit justifies risk; monitor fetal growth and amniotic fluid volume. |
| 3rd trimester | Risk of oligohydramnios, fetal hypotension, and electrolyte disturbances; avoid near term. |
Clinical note
Other ototoxic drugs may increase risk of hearing loss NSAIDs may reduce the diuretic effect Profound diuresis and electrolyte depletion can occur.
| FDA category | Animal |
| Placental transfer | Crosses placenta; fetal concentrations similar to maternal. |
| Breastfeeding |
■ FDA Black Box Warning
Furosemide is a potent diuretic; excessive diuresis may lead to profound electrolyte depletion, volume depletion, and circulatory collapse.
| Common Effects | hepatic |
| Serious Effects |
AnuriaSevere electrolyte depletionHypersensitivity to furosemide or sulfonamidesHepatic coma or pre-coma
| Precautions | Monitor for electrolyte imbalances (hypokalemia, hyponatremia, hypomagnesemia), Risk of ototoxicity, especially with rapid infusion or concurrent use of other ototoxic drugs, Monitor renal function and blood pressure; caution in patients with severe hepatic cirrhosis or renal impairment, May cause photosensitivity, blood dyscrasias, and hypersensitivity reactions |
| Food/Dietary | Avoid excessive salt intake to prevent fluid retention and counteract diuretic effect. Limit alcohol as it can increase diuretic effect and cause dehydration. May increase potassium loss; consider potassium-rich foods (bananas, oranges, spinach) unless contraindicated (e.g., with ACE inhibitors). No specific restrictions with grapefruit juice. |
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| Excreted in breast milk in low concentrations; may suppress lactation and cause electrolyte disturbances in infant; use with caution. |
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | Furosemide is pregnancy category C. First trimester: Limited human data; animal studies show no teratogenicity at clinically relevant doses, but fetal toxicity (hydronephrosis) at high doses. Second/third trimesters: Risk of electrolyte imbalance in mother and fetus, potential for decreased placental perfusion due to maternal hypovolemia. Use only if benefit outweighs risk, especially in oligohydramnios or preeclampsia. |
| Fetal Monitoring | Monitor maternal serum electrolytes (especially potassium), renal function, and blood pressure. In pregnancy, assess fetal growth and amniotic fluid volume via ultrasound, as diuretics may reduce placental perfusion. Monitor for maternal hypovolemia and dehydration. |
| Fertility Effects | Furosemide may transiently affect female fertility by altering endometrial function and ovulation due to electrolyte or volume shifts. No known specific effect on male fertility. |
| Clinical Pearls | Monitor urine output and electrolytes, especially potassium. Avoid use in anuria, severe electrolyte depletion, and hepatic coma. Can cause ototoxicity, especially with rapid IV administration or concurrent use of other ototoxic drugs. Sulfonamide allergy may cross-react; use caution. Loop diuretics like furosemide are effective in renal impairment, unlike thiazides. |
| Patient Advice | Take exactly as prescribed, preferably in the morning to avoid nighttime urination. · Weigh yourself daily and report rapid weight gain or loss. · Avoid alcohol and NSAIDs as they may reduce diuretic effect or increase kidney damage. · Report hearing loss, ringing in ears, dizziness, or muscle cramps immediately. · Do not stop suddenly without consulting your doctor; may cause rebound edema. · Limit high-potassium foods if also taking ACE inhibitors or potassium-sparing diuretics. · Stay hydrated but avoid excessive fluid intake. |