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Drug Whys [Furosemide]

Mike McEvoy

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By Mike McEvoy, Ph.D., REMT-P, RN, CCRN

Generic Name: furosemide (multiple manufacturers)

Common Brand Name: Lasix (Aventis Pharmaceuticals – U.S.)

Popularity: 18th most commonly prescribed drug in 2002 (U.S.)

Class: Short-acting loop diuretic, sulfonamide (contains sulfa), antihypertensive.

Treatment Uses

Edema resulting from liver, kidney, or heart failure or burns.

Management of high blood pressure.

Low urinary output in pregnancy complications, in conjunction with other therapies to reduce swelling of the brain, and to deliberately increase urinary output (diuresis) in certain poisonings.

Dosing and Administration

Orally, 20 to 80 mg per day titrated to effect (up to 600 mg/day). Larger doses are divided into twice daily. Single doses are best taken in the morning to prevent frequent urination from interrupting sleep. Intravenous (IV) dosing for emergency treatment of pulmonary edema varies from 40 mg to 80 mg. Best practice dosing (found in many heart failure protocols) is a single IV bolus of double the patient's usual daily (24-hour) dose. IV maximums top off at 4,000 mg/day. Injection rates faster than 20 mg/min can cause hearing impairment. One way to slowly deliver a med is to inject the drug into a proximal port of your IV tubing and allow the drip rate to slowly deliver the drug to your patient (typical IV tubing administration sets have a 10- to 20-cc fill volume). Dosing for children and infants is typically 1 mg/kg/dose. IV furosemide administered orally has a potency similar to oral tablets. In patients without IV access, IV doses can be given IM but have slower absorption. Furosemide has been nebulized to treat asthma and inhaled nasally for sinus congestion, both with good results.

Pharmacology/Pharmacokinetics/Stability

Following oral administration, diuresis occurs within 30-60 minutes, peaks in 1-2 hours, and tapers off after 6-8 hours. When given IV, the effect is faster, with diuresis starting after 2-5 minutes, peaking in 30 minutes, and tapering after 2 hours. A significant vasodilatory effect of furosemide occurs within 10 minutes of oral dosing and within seconds of IV administration. This vasodilatory effect is extremely beneficial for medics managing congestive heart failure patients in cold climates. Administration of furosemide prior to moving a patient from indoors to the ambulance can counter the vasoconstrictive effects of cold air, potentially avoiding an acute worsening of symptoms from pulmonary edema in very sick patients. Many EMS systems substitute bumetanide (Bumex), another loop diuretic, during national shortages of IV furosemide that have recently occurred. 40 mg of furosemide is approximately equal to 1 mg of bumetanide.

The kidneys excrete about 50-80% of furosemide. The remainder is eliminated by the liver or excreted unchanged in the stool. Furosemide is not removed by hemodialysis.

Although compatible with most commonly used IV solutions (D5W, NS, LR), furosemide is light sensitive; thus, it's packaged in dark vials. Tablets expire 5 years and IV expires 42 months from manufacture date. Yellowed tablets or discolored (usually yellowed) IV furosemide indicates excessive light exposure, and the yellowed drug should not be used. Furosemide should be stored at room temperature (54-86°F) and protected from freezing.

Cautions and Warnings

Furosemide should not be given to patients allergic to drugs containing sulfa.

Important Side Effects and Interactions

Furosemide is, by and large, a "friendly drug." Side effects are mostly related to diuretic effects, the most significant of which are hypotension and decreased blood potassium levels. Blood pressure and electrolyte levels should be checked frequently. For reasons poorly understood, furosemide also has a tendency to increase blood glucose levels in diabetics. Nausea occurs occasionally with oral furosemide and can usually be reduced or eliminated by taking the drug with food.