- Lasix (named for LAst SIX) is only effective for 6 hours
- Optimal dosing is given at least twice daily (patient otherwise is Sodium avid 18 hours/day)
- Oral
- Onset: 1 hour
- Half-Life: 1 to 1.5 hours
- Duration: 6 to 8 hours
- Highly variable Bioavailability on oral ingestion (typically 50%, varies between 10 and 90%)
- Increased Bioavailability when taken with meals
- Gastrointestinal absorption is markedly decreased in severe edema (e.g. CHF exacerbation)
- Contrast with Torsemide which has excellent and consistent Bioavailability
- Intravenous
- Onset: 5 minutes
- Duration: 2 hours
-
Protein-Binding: 95%
- Eliminated unchanged in urine
- Higher doses (2-3x) required for Nephrotic Syndrome
- Renal dysfunction results in decreased response and increased Half-Life
- Only 15-20% of Furosemide dose is delivered to the renal tubule in stage 5 CKD
- Start: 20 to 40 mg orally daily to twice daily
- Twice daily dosing is recommended due to short duration of activity
- Maximum: 600 mg/day (rare to exceed 400 mg/day)
- Peak effect at 1 to 1.5 hours after oral dose
- Duration: 6-8 hours
- Dosing
-
Intravenous (adults)
- Intravenous dose is typically one half of oral dose
- In exacerbations, the oral dose is often used IV
- Administer slowly over 1-2 minutes
- Doses higher than 80 mg should infuse slowly to avoid Ototoxicity
- Bolus
- Dose 20 to 40 mg IV (0.5-1.0 mg/kg, max 2 mg/kg)
- In CHF exacerbations, 60 mg IV is often given
- In Renal Insufficiency, consider starting dose = 40 * sCr
- Where sCr = Serum Creatinine
- Reflects the diminishing effect of Furosemide as Serum Creatinine increases (and GFR drops)
-
Pharmacokinetics
- Onset: Diuresis starts within 10 minutes
- Peak effect in 10-30 minutes
- Duration: 6 hours
- Peak Diuretic effect of repeat dosing is 25% of the first dose
- Compensatory Sodium retention may be overcome by frequent IV doses or continuous infusion
- Maximum effective dose (ceiling dose)
- Chronic Kidney Disease or Nephrotic Syndrome: 80 to 200 mg
- Congestive Heart Failure or Cirrhosis: 40-80 mg
- Dosing
-
Intravenous Infusion (adults)
- Background
- More effective at maintaining a constant increased Urine Output with less adverse effects (e.g. Ototoxicity)
- Maximum diuresis at 3 hours after continuous infusion started
- Precautions
- Very high dose Furosemide infusions (4 mg/min) risk Ototoxicity
- Loading dose: 40-200 mg
- Loading doses higher than 80 mg should infuse slowly to avoid Ototoxicity
- Infusion dose
- Start: 10-20 mg/hour (0.25 to 0.75 mg/kg/hour) IV
- Maximum: 40 mg/hour IV
- IV/IM/PO
- Start: 0.5 to 2 mg/kg/dose IV/IM/PO every 6 to 12 hours
- Max: 6 mg/kg/dose
- Intravenous Infusion
- Start: 0.05 mg/kg/hour and titrate
- See Loop Diuretic
- Ototoxocity
- See Loop Diuretic
- Most common with high doses or rapid infusion rates (>4 mg/min)
- Decreased Thyroid Hormone levels
- Associated with Furosemide doses >80 mg/day
-
Warfarin
- Furosemide displaces Warfarin from Protein binding and increases Warfarin levels and INR
-
Cyclosporine
-
Cyclosporine decreases Uric Acid excretion, and increased gout risk when used with Furosemide
-
Lithium
- Avoid use with Furosemide
- Agents that decrease Furosemide Diuretic effect
- Indomethacin
- Probenacid
- Pregnancy Category C
- Unknown Safety in Lactation
- (2021) Presc Lett, Resource #370507, Commonly Used Diuretics
- (2020) Med Lett Drugs Ther 62(1598): 73-80
- Hamilton (2020) Tarascon Pocket Pharmacopoeia
- Olson (2020) Clinical Pharmacology, Medmaster Miami, p. 62-3
-
Won Oh (2015) Electrolyte Blood Press 13(1):17-21 +PMID: 26240596 [PubMed]
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