What alternative diuretic can be given to a patient with a urinary tract infection (UTI) and pneumonia who is allergic to furosemide (Lasix)?

Alternative Diuretics for Furosemide Allergy

If a patient is allergic to furosemide, bumetanide is the preferred alternative loop diuretic, as the FDA label explicitly states that "successful treatment with bumetanide following instances of allergic reactions to furosemide suggests a lack of cross-sensitivity." 1

Primary Alternative: Bumetanide

Bumetanide should be your first-line alternative in patients with documented furosemide allergy. 1

• Bumetanide is FDA-approved for edema associated with congestive heart failure, hepatic and renal disease, including nephrotic syndrome 1
• The drug can be administered intravenously or intramuscularly when oral administration is not practical 1
• Clinical evidence demonstrates lack of cross-reactivity with furosemide in allergic patients 1
• Dosing: Start with 0.5-2 mg IV/IM, with almost equal diuretic response between oral and parenteral routes 2, 1

Important Caveat About Sulfonamide Cross-Reactivity

Furosemide is a sulfonamide derivative, and true IgE-mediated anaphylaxis has been documented. 3, 4

• One case report demonstrated positive intradermal testing to both furosemide and sulfamethoxazole, raising the possibility of cross-reactivity between non-aromatic sulfonamides (like furosemide) and antimicrobial sulfonamides 4
• However, this cross-reactivity mechanism has not been clearly established in the literature 4
• If the patient has a history of severe allergic reactions to sulfonamide antibiotics, consider using ethacrynic acid instead of bumetanide, as ethacrynic acid is not a sulfonamide derivative 3

Second-Line Alternative: Ethacrynic Acid

Ethacrynic acid is specifically indicated for patients allergic to sulfa drugs. 3

• Works in the medullary diluting segment of the loop of Henle, blocking active chloride reabsorption 3
• Has a "high ceiling" effect, is potent and rapidly acting with short duration 3
• Excellent for severe fluid overload or pulmonary edema 3
• This is the safest choice if there is any concern about sulfonamide cross-reactivity 3

Third-Line Alternative: Torsemide

Torsemide is another loop diuretic option with longer duration of action and better oral bioavailability than furosemide. 5

• Dosing: 10-20 mg once daily, maximum 200 mg 5
• May induce greater cumulative diuresis than furosemide due to pharmacokinetic advantages 5
• However, torsemide is also a sulfonamide derivative, so use with caution in patients with sulfa allergies 2

Sequential Nephron Blockade for Resistant Cases

If loop diuretic alternatives alone are insufficient, add thiazide or potassium-sparing diuretics for sequential nephron blockade. 5

• Add metolazone 2.5-10 mg once daily or hydrochlorothiazide 25-100 mg once or twice daily 5
• Combined hydrochlorothiazide-bumetanide therapy produces marked diuresis even in patients with azotemia (creatinine 2.3-4.9 mg/dl) who respond poorly to single agents 6
• Add spironolactone 12.5-25 mg daily (maximum 50 mg) to counteract secondary hyperaldosteronism 5
• Consider amiloride 5 mg once daily (maximum 20 mg) to directly block epithelial sodium channels 5

Critical Monitoring Requirements

Closely monitor electrolytes, renal function, and volume status regardless of which alternative diuretic is chosen. 5

• Check potassium, sodium, magnesium, and chloride levels frequently 5
• Monitor for signs of volume depletion: hypotension, tachycardia, poor skin turgor 5
• Assess renal function to detect acute kidney injury from excessive diuresis 5
• Watch for metabolic alkalosis and hypochloremia, which worsen diuretic resistance 5

Common Pitfall to Avoid

Do not assume all loop diuretics are contraindicated just because the patient is allergic to furosemide. 1

• Bumetanide has demonstrated lack of cross-sensitivity in allergic reactions to furosemide 1
• The key is determining whether the allergy is truly IgE-mediated anaphylaxis versus other adverse reactions 4
• If the reaction was severe anaphylaxis with possible sulfa cross-reactivity, ethacrynic acid is the safest alternative 3, 4