IV lasix or Furosemide is a loop diuretic that acts by inhibiting the reabsorption of sodium and chloride (via the Na/K/2Cl cotransporter) in the thick ascending limb of the loop of Henle.
IV lasix enhances the excretion of sodium, potassium, calcium, chloride, and water. IV lasix is used frequently in the intensive care unit (ICU) setting for diuresis.
Intravenous furosemide begins to work in 5 minutes, peaks at 30 minutes, and lasts for about 2 hours. The elimination half-life of IV lasix is approximately 30 to 120 minutes.
A dosing interval of 6 hours allows for four to five half-lives of elimination. Typically, with the appropriate dose of IV lasix , a maximal response will be seen within the first hour and the increased urine output will continue in a tapering fashion for up to 6 hours.
A large initial response of IV lasix followed by a rapid tapering of urine output may be an indication that the patient is not quite ready for diuresis.
The dose of IV lasix is titrated to effect, but the dose depends on renal function. Higher doses are needed with worsening renal function. IV lasix acts in the loop of Henle, so the effect seen after a dose of furosemide depends on the rate at which blood is filtered through the glomerulus.
As creatinine clearance decreases (implying lower glomerular filtration rate [GFR] and worse renal function), a higher dose of furosemide is needed to achieve a timely response. If the dose of furosemide administered is too low for a given creatinine clearance, then a delayed diuretic response can be seen.
Watch Out For
The main toxicities of IV lasix include ototoxicity, electrolyte abnormalities, and allergic reactions. Ototoxicity is more common with very high doses of furosemide and the mechanism is thought to be due to the presence of a similar Na/K/2Cl cotransporter in the inner ear.
Electrolyte abnormalities from the diuresis induced by IV lasix include hypokalemia, hyponatremia, and metabolic alkalosis. Overly aggressive diuresis can lead to elevated blood urea nitrogen (BUN) and creatinine as well as hypotension.
The presence of allergic reactions to IV lasix do occur; however, many clinicians doubt the existence of a true sulfa allergic reaction. Purported allergic reactions can be as mild as a rash or as serious as anaphylaxis or Stevens-Johnson syndrome.
One final note is that when thinking about the clinical effects of furosemide, the astute clinician will remember that the brand name was chosen in part based on the duration of the medication lasting six hours; hence, the name Lasix
Further Readings
Micromedex. Martindale ”The Complete Drug Reference: Furosemide. USP DI Drug Information for the Health Care Professional: Diuretics, Loop http://www.thomsonhc.com/hcs/librarian.
Rose B. Optimal dosage and side effects of loop diuretics. UpToDate. 2005. http://www.uptodate.com/physicians/pulmonology toclist.asp