Furosemide

Article Author:
Tahir Khan
Article Editor:
Abdul Siddiqui
Updated:
10/27/2018 12:31:35 PM
PubMed Link:
Furosemide

Indications

The Food and Drug Administration (FDA) has approved the use of furosemide in treatment of conditions with volume overload and edema secondary to congestive heart failure exacerbation, liver failure, or renal failure including the nephrotic syndrome.  

Patients with acutely decompensated heart failure (ADHF) with volume overload who have not received diuretics previously, the initial dose of furosemide should be 20 to 40 mg intravenously, and later, titrate the furosemide dose according to the clinical response of the patients. However, those patients with ADHF with a normal kidney function who are on chronic diuretic therapy, the initial dose of furosemide can be initiated as an equivalent to or greater than the total oral maintenance dose of furosemide patient takes per day. Subsequently, the diuretic dose is adjusted according to the clinical response of the patient. Nevertheless, the starting with higher doses of furosemide, that is, at a dose of 2.5 times the total daily oral dose of furosemide per day, has shown a significant trend toward a rapid improvement in the global assessment of patients’ symptoms.

Although FDA approved, the use of loop diuretics alone or in combination with other anti-hypertensive medications is an alternative to thiazide diuretics to treat hypertension. However, the clinical guidelines panel report of Eighth Joint National Committee (JNC-8) published in 2014 and the American College of Cardiology/American Heart Association (ACC/AHA) Task Force Panel Guidelines on hypertension treatment published in 2017 does not include the use of loop diuretic as a first-line medication to treat hypertension. Furosemide can be used as a second-line agent in heart failure patients with symptoms and patients with advanced kidney disease with estimated glomerular filtration rate less than 30 ml per minute, the loop diuretics (furosemide) are preferred over thiazide diuretics to treat hypertension. 

In patients with liver cirrhosis and ascites, diuretic therapy is recommended accompanied by dietary sodium restriction. The recommended diuretics are a combination of spironolactone and furosemide starting at a ratio of 100 mg of spironolactone and 40 mg of furosemide. They are titrated up to the dose of diuretics in increment of the same ratio until the adequate response to diuretic therapy is achieved, or a maximum dose of 400 mg of spironolactone plus 160 mg of furosemide is reached. Diuretics can be started at relatively lower doses of 50 mg of spironolactone with 20 mg of furosemide in cases of intolerance to diuretics secondary to borderline blood pressure.

Mechanism of Action

Furosemide inhibits tubular reabsorption of sodium and chloride in the proximal and distal tubules, as well as in the thick ascending loop of Henle by inhibiting sodium-chloride cotransport system resulting in excessive excretion of water along with sodium, chloride, magnesium, and calcium.

Administration

Furosemide is available in the oral and intravenous formulations. Oral furosemide can be administered in the form of tablets or oral solution. Intravenous furosemide is twice as potent as oral furosemide.

In patients with the normal renal function the oral dose equivalence of furosemide relative to other oral diuretics is as follows:

  • 40 mg of furosemide = 20 mg of torsemide = 1 mg of bumetanide
  • Furosemide oral tablet formulations are available in 20 mg, 40 mg, and 80 mg dosages.
  • Furosemide oral solution is available as 10 mg of furosemide per ml formulation or 8 mg per ml, i.e., 40 mg furosemide per 5 ml of solution.

Furosemide glucuronide is a major biotransformation active product of furosemide having an active diuretic effect. In healthy individuals, 91% to 99% of furosemide is bound to plasma protein especially albumin. Only 2.3% to 4.1% of furosemide is existent in an unbound form in therapeutic concentrations.

The onset of action of furosemide is usually within the first hour of oral furosemide intake, and it takes first 1 to 2 hours to achieve a peak effect. The mean bioavailability of oral furosemide is 60% to 64% compared with the bioavailability of intravenously administered furosemide. Although more furosemide is excreted in the urine after IV administration, there is no difference in the amount of unchanged furosemide excretion in urine between the 2 oral formulations. Oral solution form of furosemide is more avidly absorbed compared to oral tablets formulation to achieve a peak therapeutic level in 50 minutes versus 87 minutes, respectively. However, the peak plasma therapeutic levels achieved and area under the plasma concentration-time curve is similar between two formulations. Peak plasma concentration increases proportionately with the increasing doses of furosemide, but time-to-peak plasma levels do not vary corresponding to different doses. The terminal half-life of furosemide is approximately 2 hours and total time of therapeutic effect is 6 to 8 hours.

Adverse Effects

Hypokalemia, hypomagnesemia, hypocalcemia, hyperglycemia, glycosuria, hyperuricemia, hypertriglyceridemia, increased cholesterol levels, orthostatic hypotension,  vasculitis, thrombophlebitis, dizziness, vertigo, headache, paresthesia, hearing impairment, tinnitus, dehydration,  muscle cramps, abdominal cramping, anorexia, constipation or diarrhea, pancreatitis, hepatic encephalopathy, anemia, aplastic anemia, eosinophilia, agranulocytosis, hemolytic anemia, interstitial nephritis, renal injury, hypersensitivity reactions, anaphylaxis, skin photosensitivity, bullous pemphigoid, erythema multiforme, exfoliative dermatitis, acute generalized exanthematous pustulosis, steven johnson syndrome, toxic epidermal necrolysis, urticaria, and fever.

Contraindications

Furosemide use is contraindicated in patients with documented allergy to furosemide and patients with anuria.

Monitoring

Caution should be practiced in use of Furosemide.

There is a black box warning suggesting the cautious use of furosemide as it is a potent diuretic, can predispose to excessive loss of water and electrolytes resulting in dehydration with electrolyte depletion.

According to Beers Criteria, caution should be practiced in administering diuretics to patients 65 years and older to avoid potential adverse effects of inducing hyponatremia by causing or exacerbating syndrome of inappropriate antidiuretic hormone secretion (SIADH); therefore, close monitoring of serum sodium is advisable at initiation or during the dose adjustment in older adults.

Ototoxicity can occur with use of furosemide, but the following conditions predispose patients to a higher risk of reversible or irreversible hearing impairment:

  • Use of a higher than the recommended dose of furosemide or a fast infusion rate of the drug,
  • Hypoalbuminemic comorbid illnesses
  • The concomitant use of ethacrynic acid, aminoglycosides, or other ototoxic drugs
  • Patients with underlying severe renal impairment

Caution should be practiced in patients with underlying liver disease especially those with the decompensated liver disease as rapid electrolytes imbalance secondary to furosemide use can precipitate hepatic encephalopathy and hepatic coma. In patients with hepatic coma, the furosemide use should be delayed till improvement in the mental status of the patient.

In patients with an advanced renal disease with fluid overload the patients should be closely monitored for oliguria, azotemia and volume status; and if either of oliguria or azotemia develops the furosemide should use should be discontinued to prevent kidney injury.

High-risk patients for radiocontrast-induced nephropathy are more predisposed to having a worsened kidney function if furosemide is given prior to contrast administration as compared to the high-risk patients receiving gentle hydration before contrast exposure.

Patients with a known history of urinary retention due to, for example, benign prostatic hyperplasia, or neurogenic bladder with bladder evacuation abnormalities, or urethral and ureteral strictures, should be observed closely during initial days of furosemide treatment and thereafter for worsening of symptoms as excessive diuresis and retention of urine can lead to acute urinary retention leading to acute kidney injury.

Risk of hypokalemia is increased with the use of high dose of furosemide, decreased oral intake of potassium, in patients with hyperaldosterone state (liver abnormalities or licorice ingestion) or concomitant use of corticosteroid, ACTH, and laxatives.

Furosemide at high doses, i.e., more than 80 mg per day inhibits thyroid hormone binding to thyroid binding protein leading to a transient increase in free thyroid hormones that subsequently causes a mild decrease in total thyroid hormone.

Furosemide is a pregnancy category C drug and should be used with caution in pregnant women after discussion with the patient about risk and benefits.

Toxicity

Hypokalemia, hypomagnesemia, hypocalcemia, hyperglycemia, glycosuria, hyperuricemia, hypertriglyceridemia, increased cholesterol levels, orthostatic hypotension,  vasculitis, thrombophlebitis, dizziness, vertigo, headache, paresthesia, hearing impairment, tinnitus, dehydration,  muscle cramps, abdominal cramping, anorexia, constipation or diarrhea, pancreatitis, hepatic encephalopathy, anemia, aplastic anemia, eosinophilia, agranulocytosis, hemolytic anemia, interstitial nephritis, renal injury, hypersensitivity reactions, anaphylaxis, skin photosensitivity, bullous pemphigoid, erythema multiforme, exfoliative dermatitis, acute generalized exanthematous pustulosis, steven johnson syndrome, toxic epidermal necrolysis, urticaria, and fever.