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Inj lasix

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Inj. Lasix (Furosemide Injection)

Class: Loop diuretic (most commonly used of this class)

Mechanism of Action

Furosemide inhibits the Na+/K+/2Cl- cotransporter in the luminal membrane of the ascending limb of the loop of Henle. This blocks reabsorption of these ions, lowers medullary osmotic pressure, and reduces water reabsorption from the descending limb, producing diuresis. Because the ascending limb normally reabsorbs 25-30% of filtered NaCl and downstream segments cannot compensate for the increased Na+ load, loop diuretics produce the greatest diuretic effect of all diuretic classes - even in patients with poor renal function or those unresponsive to other diuretics (Lippincott Illustrated Reviews: Pharmacology, p. 337-338).
The drug must be secreted into the tubular lumen at the proximal convoluted tubule to act, so its effect depends on adequate renal secretion. NSAIDs can blunt its diuretic action by inhibiting renal prostaglandin synthesis.

Indications

  • Edema of cardiac, hepatic, or renal origin (CHF, cirrhosis, nephrotic syndrome)
  • Acute pulmonary edema
  • Hypertensive emergencies (adjunct)
  • Hypercalcemia
  • Oliguria/hyperkalemia in select settings

Dosing/Administration (IV)

  • Dosing is highly individualized because loop diuretics follow a sigmoidal ("S"-shaped) dose-response curve with a threshold, a steep rapid-rise phase, and a ceiling effect. Doses below the patient's threshold produce no diuresis; doses above the ceiling add no extra effect - once an effective dose is found, frequency (not dose) is adjusted to titrate daily diuresis.
  • For a hospitalized patient being converted from oral to IV dosing for hypervolemia, a common approach is an initial IV dose of about 2 to 2.5 times the chronic oral dose (bioavailability of oral furosemide is reduced, roughly 50%, so IV dosing needs adjustment).
  • Can be given as IV push (slowly, typically over 1-2 minutes per standard dose) or continuous infusion in refractory cases.
  • Onset with IV administration is rapid (minutes), duration of action is roughly 6 hours.

Adverse Effects / Nursing Considerations

  • Hypokalemia, hypomagnesemia, hyponatremia (electrolyte loss from blocking Na/K/2Cl transport)
  • Hypotension/volume depletion, ototoxicity (especially with rapid IV push or high doses, more common with ethacrynic acid but seen with furosemide too)
  • Hyperuricemia, hyperglycemia
  • Metabolic alkalosis (chloride-responsive) can occur with loop diuretic use due to increased Na+ delivery to the distal nephron enhancing H+ secretion (Tietz Textbook of Laboratory Medicine, 7th ed.)
  • Monitor: serum electrolytes (K+, Mg2+, Na+), renal function, blood pressure, fluid balance/urine output, hearing (with high-dose IV therapy)
  • Note: brand name "Lasix" reflects that its diuretic effect "lasts six" hours.
If this is for a specific patient scenario (e.g., dose calculation, CHF exacerbation, renal impairment dosing, or drug interactions), let me know the clinical context and I can go into that in more depth.
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