Furosemide

Aka: Furosemide, Lasix

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II. Indications

  1. See Loop Diuretic

III. Precautions

  1. Lasix (named for LAst SIX) is only effective for 6 hours
  2. Optimal dosing is given at least twice daily (patient otherwise is Sodium avid 18 hours/day)

IV. Pharmacokinetics

  1. Oral
    1. Onset: 1 hour
    2. Half-Life: 1 to 1.5 hours
    3. Duration: 6 to 8 hours
    4. Highly variable Bioavailability on oral ingestion (typically 50%, varies between 10 and 90%)
      1. Increased Bioavailability when taken with meals
      2. Gastrointestinal absorption is markedly decreased in severe edema (e.g. CHF exacerbation)
      3. Contrast with Torsemide which has excellent and consistent Bioavailability
  2. Intravenous
    1. Onset: 5 minutes
    2. Duration: 2 hours
  3. Protein-Binding: 95%
  4. Eliminated unchanged in urine
  5. Higher doses (2-3x) required for Nephrotic Syndrome
  6. Renal dysfunction results in decreased response and increased Half-Life
    1. Only 15-20% of Furosemide dose is delivered to the renal tubule in stage 5 CKD

V. Mechanism

  1. See Loop Diuretic

VI. Dosing: Oral (adults)

  1. Start: 20 to 40 mg orally daily to twice daily
    1. Twice daily dosing is recommended due to short duration of activity
  2. Maximum: 600 mg/day (rare to exceed 400 mg/day)
  3. Peak effect at 1 to 1.5 hours after oral dose
  4. Duration: 6-8 hours

VII. Dosing: Intravenous (adults)

  1. Intravenous dose is typically one half of oral dose
    1. In exacerbations, the oral dose is often used IV
  2. Administer slowly over 1-2 minutes
    1. Doses higher than 80 mg should infuse slowly to avoid Ototoxicity
  3. Bolus
    1. Dose 20 to 40 mg IV (0.5-1.0 mg/kg, max 2 mg/kg)
    2. In CHF exacerbations, 60 mg IV is often given
    3. In Renal Insufficiency, consider starting dose = 40 * sCr
      1. Where sCr = Serum Creatinine
      2. Reflects the diminishing effect of Furosemide as Serum Creatinine increases (and GFR drops)
  4. Pharmacokinetics
    1. Onset: Diuresis starts within 10 minutes
    2. Peak effect in 10-30 minutes
    3. Duration: 6 hours
  5. Peak Diuretic effect of repeat dosing is 25% of the first dose
    1. Compensatory Sodium retention may be overcome by frequent IV doses or continuous infusion
  6. Maximum effective dose (ceiling dose)
    1. Chronic Kidney Disease or Nephrotic Syndrome: 80 to 200 mg
    2. Congestive Heart Failure or Cirrhosis: 40-80 mg

VIII. Dosing: Intravenous Infusion (adults)

  1. Background
    1. More effective at maintaining a constant increased Urine Output with less adverse effects (e.g. Ototoxicity)
    2. Maximum diuresis at 3 hours after continuous infusion started
  2. Precautions
    1. Very high dose Furosemide infusions (4 mg/min) risk Ototoxicity
  3. Loading dose: 40-200 mg
    1. Loading doses higher than 80 mg should infuse slowly to avoid Ototoxicity
  4. Infusion dose
    1. Start: 10-20 mg/hour (0.25 to 0.75 mg/kg/hour) IV
    2. Maximum: 40 mg/hour IV

IX. Dosing: Child

  1. IV/IM/PO
    1. Start: 0.5 to 2 mg/kg/dose IV/IM/PO every 6 to 12 hours
    2. Max: 6 mg/kg/dose
  2. Intravenous Infusion
    1. Start: 0.05 mg/kg/hour and titrate

X. Adverse Effects

  1. See Loop Diuretic
  2. Ototoxocity
    1. See Loop Diuretic
    2. Most common with high doses or rapid infusion rates (>4 mg/min)
  3. Decreased Thyroid Hormone levels
    1. Associated with Furosemide doses >80 mg/day

XI. Drug Interactions

  1. Warfarin
    1. Furosemide displaces Warfarin from Protein binding and increases Warfarin levels and INR
  2. Cyclosporine
    1. Cyclosporine decreases Uric Acid excretion, and increased gout risk when used with Furosemide
  3. Lithium
    1. Avoid use with Furosemide
  4. Agents that decrease Furosemide Diuretic effect
    1. Indomethacin
    2. Probenacid

XII. Safety

  1. Pregnancy Category C
  2. Unknown Safety in Lactation

XIII. Resources

  1. Furosemide Tablets (DailyMed)
    1. https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=e3a5db0e-bf6c-4ea9-9133-c3f215c856d0
  2. Furosemide Intravenous Solution (DailyMed)
    1. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=39fd32f2-6bb7-4a65-d298-e48d26bc80c7

XIV. References

  1. (2021) Presc Lett, Resource #370507, Commonly Used Diuretics
  2. (2020) Med Lett Drugs Ther 62(1598): 73-80
  3. Hamilton (2020) Tarascon Pocket Pharmacopoeia
  4. Olson (2020) Clinical Pharmacology, Medmaster Miami, p. 62-3
  5. Won Oh (2015) Electrolyte Blood Press 13(1):17-21 +PMID: 26240596 [PubMed]

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Related Studies

Cost: Medications

furosemide (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing)
FUROSEMIDE 10 MG/ML SOLUTION Generic $0.09 per ml
FUROSEMIDE 100 MG/10 ML VIAL Generic $0.34 per ml
FUROSEMIDE 20 MG TABLET Generic $0.03 each
FUROSEMIDE 40 MG TABLET Generic $0.03 each
FUROSEMIDE 40 MG/4 ML VIAL Generic $0.34 per ml
FUROSEMIDE 80 MG TABLET Generic $0.05 each
lasix (on 2/22/2023 at Medicaid.Gov Survey of pharmacy drug pricing)
LASIX 40 MG TABLET Generic $0.03 each
FPNotebook does not benefit financially from showing this medication data or their pharmacy links. This information is provided only to help medical providers and their patients see relative costs. Insurance plans negotiate lower medication prices with suppliers. Prices shown here are out of pocket, non-negotiated rates. See Needy Meds for financial assistance information. GoodRx is another tool for finding lower drug prices.

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