Educational use only. Drug cards are AI-assisted study material for NCLEX preparation.
Mechanism of action
Inhibits the Na+/K+/2Cl⁻ cotransporter in the thick ascending limb of the loop of Henle, causing rapid and large-volume diuresis. Also reduces preload via venodilation. Used for fluid overload from heart failure, pulmonary edema, cirrhosis, and renal disease.
Adverse effects
Life-threatening / NCLEX-tested
- Severe hypokalemia → cardiac arrhythmias (especially dangerous in patients on digoxin)
- Profound hypotension and dehydration with rapid IV push
- Ototoxicity (tinnitus, hearing loss) — risk rises with rapid IV push and high doses
- Hyponatremia, hypomagnesemia, hypocalcemia, hypochloremic metabolic alkalosis
- Acute kidney injury from over-diuresis
- Sulfa allergy cross-reactivity (rare but reported)
Side effects
Common — what to teach
- Frequent urination (time the morning dose so it doesn't wake the patient at night)
- Dizziness, lightheadedness on standing
- Muscle cramps (often a clue to low K+ or Mg++)
- Increased thirst, dry mouth
- Hyperuricemia and possible gout flare
- Hyperglycemia
Food & drug interactions
Combined with digoxin → hypokalemia from furosemide drives digoxin toxicity. Lithium clearance falls — risk of lithium toxicity. NSAIDs blunt the diuretic effect. Aminoglycosides (gentamicin) plus furosemide multiply ototoxicity risk. ACE inhibitors and ARBs compound first-dose hypotension. Encourage potassium-rich foods (banana, orange, potato, spinach) unless contraindicated.
Nursing implications
Assessment, monitoring, patient teaching
- Monitor daily weight (same scale, same time, same clothing) — most reliable measure of fluid status; report a gain of > 2 lb in 24 h or > 5 lb in a week
- Monitor strict I&O, BP (lying and standing for orthostasis), and serum electrolytes — especially K+ and Mg++
- Push IV slowly (no faster than 20 mg/min, or 4 mg/min for high doses) to reduce ototoxicity risk
- Give in the morning to avoid nocturia; if BID, give the second dose by mid-afternoon
- Teach foods rich in potassium and how to recognize hypokalemia (muscle cramps, weakness, palpitations)
- Monitor blood glucose in diabetics; furosemide can raise it
When to hold / contraindications
- Serum K+ < 3.5 mEq/L (correct first)
- SBP < 90 mmHg or symptomatic hypotension
- Anuria (no urine output)
- Significant hypovolemia or dehydration
- Worsening renal function (rising creatinine) without provider direction
Memory anchor
"Lasix LOSES — Loses K+, Loses Na+, Loses Ca++, Loses fluid; gives Lots of pee." Daily weights are the truth-teller; 1 L of fluid ≈ 2.2 lb.
Practice Furosemide questions
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