FUROSEMIDE (Lasix)

Furosemide (Lasix) is a potent loop diuretic commonly prescribed for the management of fluid retention (edema) and hypertension. It acts by inhibiting the Na+/K+/2Cl− symporter in the thick ascending limb of the loop of Henle, promoting sodium, chloride, potassium, and water excretion.

Uses

Edema: Management of edema associated with heart failure, hepatic cirrhosis, renal disease, and nephrotic syndrome.
Hypertension: Treatment of hypertension, particularly in patients with renal impairment or heart failure.
Acute Pulmonary Edema: Reduces fluid overload in cases of acute pulmonary edema.
Hypercalcemia: Used in conjunction with hydration to manage hypercalcemia by promoting calcium excretion.
Hyperkalemia: Promotes potassium excretion in the acute management of hyperkalemia.
Ascites: Management of ascites associated with liver cirrhosis.
Acute Kidney Injury (AKI): Used to manage fluid overload, though not recommended to prevent or treat AKI.

Dosage and Administration

Edema and Heart Failure:
- Adults: 20-80 mg/day PO or IV. Increase by 20-40 mg every 6-8 hours until the desired effect.
- Pediatrics: 1 mg/kg/dose (max 6 mg/kg/day).
Hypertension:
- Adults: 40 mg twice daily.
Acute Pulmonary Edema:
- Adults: 40 mg IV. If no response, 80 mg IV after 1 hour.
Hypercalcemia:
- Adults: 80-100 mg IV every 1-2 hours with saline infusion.
Hyperkalemia:
- Adults: 40-80 mg IV as a single dose, in combination with other treatments to promote potassium excretion.
Infusion Dose (IV):
- Adults: 0.1 mg/kg/hour, titrate as needed. Max rate: 4 mg/min to avoid ototoxicity.
- Pediatrics: Initial continuous infusion rate of 0.05-0.2 mg/kg/hour, titrate as needed based on response.
Renal Dosing:
- In severe renal impairment (GFR < 30 mL/min), higher doses may be needed (up to 1000 mg/day) due to decreased tubular secretion.

Dose Adjustment in Different Diseases

Hepatic Impairment: Start with lower doses; monitor fluid and electrolyte balance closely.
Renal Impairment: Higher doses may be required due to impaired drug excretion.
Heart Failure: Gradual dose titration to avoid hypotension and electrolyte imbalances.

Drug Combinations in Use

With ACE Inhibitors: Monitor for hypotension and renal function.
With Potassium-Sparing Diuretics: Helps maintain potassium levels.
With Digoxin: Monitor potassium levels to avoid digoxin toxicity.
With NSAIDs: Reduced efficacy due to renal prostaglandin inhibition.

Presentation or Form

Tablets: 20 mg, 40 mg, 80 mg.
Injection: 10 mg/mL in 2 mL or 10 mL vials.
Oral Solution: 10 mg/mL.

Pharmacokinetics

Absorption: Rapidly absorbed after oral administration (bioavailability 50-70%).
Distribution: Plasma protein binding ~95%.
Metabolism: Minimal hepatic metabolism.
Excretion: Primarily excreted unchanged in urine.
Half-Life: 0.5-2 hours (increased in renal impairment).

Pharmacodynamics

Mechanism of Action: Inhibits the Na+/K+/2Cl− symporter in the thick ascending limb of the loop of Henle, increasing sodium, chloride, potassium, and water excretion.
Onset and Duration:
- Onset: 30-60 minutes (oral); 5 minutes (IV).
- Duration: 6-8 hours (oral); 2 hours (IV).

Drug Interactions

Aminoglycosides: Increased risk of ototoxicity.
NSAIDs: May reduce diuretic efficacy.
ACE Inhibitors: Can increase the risk of hypotension.
Lithium: Increased risk of lithium toxicity due to decreased renal clearance.
Antidiabetic Agents: Reduced efficacy of antidiabetic medications.

Comparison with Other Drugs in the Same Category

Drug	Potency	Duration	Key Feature	Common Use
Furosemide	Moderate	6-8 hours	Rapid onset	Edema, hypertension
Bumetanide	High	4-6 hours	More potent than furosemide	Severe edema
Torsemide	High	12-16 hours	Longer duration	Hypertension, heart failure
Ethacrynic Acid	Moderate	6-8 hours	No sulfonamide allergy risk	Edema

Precautions and Special Considerations

Elderly: Increased sensitivity to hypotension and electrolyte disturbances; monitor closely.
Renal Impairment: Higher doses may be required, but monitor renal function closely.
Hepatic Impairment: Monitor for fluid and electrolyte imbalance.
Pregnancy: Category C; use only if benefits outweigh risks.
Lactation: Excreted in breast milk; use with caution.

Side Effects

Common: Hypokalemia, hypotension, dehydration, hyperglycemia, dizziness.
Serious: Ototoxicity (especially with rapid IV administration), nephrotoxicity, metabolic alkalosis, hypomagnesemia, hyponatremia.

Recent Updates and Guidelines

2023 ACC/AHA Guidelines: Emphasize the importance of monitoring renal function and electrolytes during therapy.
New Formulations: Development of sustained-release formulations for improved compliance.

Facts to Remember

Monitor electrolytes (especially potassium, sodium, and magnesium) during therapy.
Avoid rapid IV administration to prevent ototoxicity.
Adjust doses based on renal function.
Be cautious of drug interactions, especially with NSAIDs and aminoglycosides.