Furosemide

Action

Unclear. Thought to inhibit sodium and chloride reabsorption from ascending loop of Henle and distal renal tubules. Increases potassium excretion and plasma volume, promoting renal excretion of water, sodium, chloride, magnesium, hydrogen, and calcium.

Availability

Injection: 10 mg/ml

Oral solution: 10 mg/ml, 40 mg/5 ml

Tablets: 20 mg, 40 mg, 80 mg

Indications and dosages

➣ Acute pulmonary edema

Adults: 40 mg I.V. given over 1 to 2 minutes. If adequate response doesn't occur within 1 hour, give 80 mg I.V. over 1 to 2 minutes.

➣ Edema caused by heart failure, hepatic cirrhosis, or renal disease

Adults: Initially, 20 to 80 mg/day P.O. as a single dose; may increase in 20- to 40-mg increments P.O. q 6 to 8 hours until desired response occurs. Thereafter, may give once or twice daily. For maintenance, dosage may be reduced in some patients or carefully titrated upward to 600 mg P.O. daily in severe edema. Usual I.M. or I.V. dosage is 20 to 40 mg as a single injection; if response inadequate, second and each succeeding dose may be increased in 20-mg increments and given no more often than q 2 hours until desired response occurs. Single dose may then be given once or twice daily.

Infants and children: 2 mg/kg P.O. (oral solution) as a single dose. As necessary, increase in increments of 1 or 2 mg/kg q 6 to 8 hours to a maximum of 6 mg/kg/dose. For maintenance, give minimum effective dosage.

➣ Hypertension

Adults: 40 mg P.O. b.i.d. If satisfactory response doesn't occur, other antihypertensives may be added before furosemide dosage is increased. However, dosage may be titrated upward as needed and tolerated to a maximum of 240 mg P.O. daily in two or three divided doses.

Off-label uses

• Hypercalcemia associated with cancer

Contraindications

• Hypersensitivity to drug or other sulfonamides

• Anuria

Precautions

Use cautiously in:

• diabetes mellitus, severe hepatic disease

• elderly patients

• pregnant or breastfeeding patients

• neonates.

Administration

• Know that I.V. or I.M. injection is given when patient requires rapid onset of diuresis or can't receive oral doses.

• Be aware that I.V. dose may be given by direct injection over 1 to 2 minutes.

• For I.V. infusion, dilute in dextrose 5% in water, normal saline solution, or lactated Ringer's solution.

☞ Don't infuse more than 4 mg/minute.

• Give oral doses in morning with food. If second dose is prescribed, give in afternoon.

Adverse reactions

CNS: dizziness, headache, vertigo, weakness, lethargy, paresthesia, drowsiness, restlessness, light-headedness

CV: hypotension, orthostatic hypotension, tachycardia, volume depletion, necrotizing angiitis, thrombophlebitis, arrhythmias

EENT: blurred vision, xanthopsia, hearing loss, tinnitus

GI: nausea, vomiting, diarrhea, constipation, dyspepsia, oral and gastric irritation, cramping, anorexia, dry mouth, acute pancreatitis

GU: excessive and frequent urination, nocturia, glycosuria, bladder spasm, oliguria, interstitial nephritis

Hematologic: anemia, purpura, leukopenia, thrombocytopenia, hemolytic anemia

Hepatic: jaundice

Metabolic: hyperglycemia, hyperuricemia, dehydration, hypokalemia, hypomagnesemia, hypocalcemia, alkalosis

Musculoskeletal: muscle pain, muscle cramps

Skin: photosensitivity, rash, diaphoresis, urticaria, pruritus, exfoliative dermatitis, erythema multiforme

Other: fever, transient pain at I.M. injection site

Interactions

Drug-drug. Aminoglycosides, ethacrynic acid, other ototoxic drugs: increased risk of ototoxicity

Amphotericin B, corticosteroids, corticotropin, potassium-wasting diuretics, stimulant laxatives: additive hypokalemia

Antihypertensives, diuretics, nitrates: additive hypotension

Cardiac glycosides: increased risk of glycoside toxicity and fatal arrhythmias

Clofibrate: exaggerated diuretic response, muscle pain and stiffness

Hydantoins, nonsteroidal anti-inflammatory drugs, probenecid: diuresis inhibition

Insulin, oral hypoglycemics: decreased hypoglycemic effect

Lithium: decreased lithium excretion, possible toxicity

Norepinephrine: decreased arterial response to norepinephrine

Propranolol: increased propranolol blood level

Salicylates: increased risk of salicylate toxicity at lower dosages than usual

Succinylcholine: potentiation of succinylcholine effect

Sucralfate: decreased naturietic and antihypertensive effects of furosemide

Sulfonylureas: decreased glucose tolerance, resulting in hyperglycemia

Theophyllines: altered, enhanced, or inhibited theophylline effects

Tubocurarine: antagonism of tubocurarine effects

Drug-diagnostic tests. Blood urea nitrogen (BUN): transient increase

Calcium, magnesium, platelets, potassium, sodium: decreased levels

Cholesterol, creatinine, glucose, nitrogenous compounds: increased levels

Drug-herbs. Dandelion: interference with drug's diuretic effect

Ephedra (ma huang), ginseng: decreased furosemide efficacy

Licorice: rapid potassium loss

Drug-behaviors. Acute alcohol ingestion: additive hypotension

Sun exposure: increased risk of photosensitivity

Patient monitoring

• Watch for signs and symptoms of ototoxicity.

☞ Assess for other evidence of drug toxicity (arrhythmias, renal dysfunction, abdominal pain, sore throat, fever).

• Monitor CBC, BUN, and electrolyte, uric acid, and CO₂ levels.

• Monitor blood pressure, pulse, fluid intake and output, and weight.

• Assess blood glucose levels in patients with diabetes mellitus.

• Monitor dietary potassium intake. Watch for signs and symptoms of hypokalemia.

Patient teaching

• Instruct patient to take in morning with food (and second dose, if prescribed, in afternoon), to prevent nocturia.

• Tell patient that drug may cause serious interactions with many common drugs. Instruct him to tell all prescribers he's taking it.

• Instruct patient to report signs and symptoms of ototoxicity (hearing loss, ringing in ears, vertigo) and other drug toxicities.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.

• Instruct patient to move slowly when rising, to avoid dizziness from sudden blood pressure decrease.

• Encourage patient to discuss need for potassium and magnesium supplements with prescriber.

• Caution patient to avoid alcohol and herbs while taking this drug.

• Inform patient that he'll undergo regular blood testing during therapy.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, herbs, and behaviors mentioned above.

g