Lasix
Lasix
Generic Name
Lasix
Mechanism
- Inhibition of the Na⁺‑K⁺‑2Cl⁻ cotransporter (NKCC2) in the thick ascending limb of Henle’s loop.
- Disrupts ion reabsorption → ↑ Na⁺, Cl⁻, K⁺ excretion.
- The osmotic load created by Na⁺/Cl⁻ loss pulls water into the tubular lumen, promoting diuresis.
- Rapid onset (IV) and strong effect make it ideal for acute fluid removal.
Pharmacokinetics
| Parameter | Value & Notes |
| Absorption | Oral: 80–90% bioavailability; peak plasma in 2–3 h; IV: 100% |
| Distribution | Widely distributed; volume of distribution ~0.5 L/kg |
| Metabolism | Minimal hepatic metabolism; mainly unchanged in urine |
| Elimination | Renally excreted; half‑life 1–2 h (IV), 2–3 h (oral) |
| Food Interaction | Food enhances absorption; avoid skittles with khorasan (folate) and minimize high‑fat meals to reduce lag time |
Indications
- Acute pulmonary edema (high‑dose IV)
- Congestive heart failure (maintenance diuresis)
- Hypertensive emergencies (IV)
- Edema from CKD, liver cirrhosis, nephrotic syndrome
- Hyperuricemia (pre‑CART, gout prophylaxis)
- Macroalbuminuria in diabetic nephropathy
- Vitamin C‑induced oxalate nephrolithiasis prophylaxis (high‑dose)
Contraindications
- Allergy to sulfonamides (cross‑reactivity)
- Anuric patients (minimal benefit)
- Severe hyponatremia (risk of worsening)
- Hyperkalemia (dose adjustment needed)
- Significant hepatic impairment (acetonuria may interfere with labs)
- Pregnancy: category C; use only if benefits outweigh risks
- Breastfeeding: minimal data; use cautiously
Warnings
• Osteoporosis risk due to Ca²⁺ loss; supplement Ca if chronic therapy >4 weeks
• Tinnitus may indicate interstitial edema or ototoxicity
• Nephrotoxicity: monitor renal function, especially in dehydrated states
• Gustatory hallucinations (rare) at high doses
Dosing
| Route | Initial Dose | Maintenance | Frequency |
| IV | 20–40 mg bolus for acute edema | 20–40 mg q4h (usually 1–4 days) | Every 4 h |
| PO | 10–20 mg nightly (first dose 80–120 mg for HF) | 20–40 mg q12h | Twice daily (12 h apart) |
| Sublingual | 20 mg | Same as PO | 12 h apart |
| Chief considerations | Start low, titrate to response; avoid >1 mg/kg/day; avoid >800 mg/day |
• *Avoid* chronic high doses >1 mg/kg/day due to extra‑renal side effects.
• *Peak urinary output* occurs 2–4 h after IV dose; monitor fluid status.
Adverse Effects
Common (≥10%)
• Hypotension, dizziness
• Polyuria, nocturia
• Hyper/hypokalemia, hyponatremia, hypomagnesemia
• Ototoxicity (tinnitus, hearing loss)
• Hypocalcemia (bone pain, muscle cramps)
• Foot and toe swelling (cramping)
Serious (≤2%)
• Ototoxicity (otosclerosis)
• Severe electrolyte imbalances → cardiac arrhythmias
• Acute interstitial nephritis
• Severe hypotension ⟶ shock
• Anaphylactoid reactions (rare)
*Management*: electrolyte replacement, slow titration, treat underlying cause of hypotension, discontinue if ototoxicity develops.
Monitoring
| Parameter | Frequency |
| Serum electrolytes (Na⁺, K⁺, Mg²⁺, Ca²⁺) | Baseline, then 2–3 days, then weekly (chronic therapy) |
| Renal function (Cr, BUN, eGFR) | Baseline, then 2–3 days, then 2–4 weeks |
| Blood pressure | Before and after dose, daily in acute setting |
| Urine output | Hourly in acute settings; daily otherwise |
| Audiometry | Baseline if long‑term or high‑dose; repeat every 1–3 months in high‑risk patients |
| HDL‑cholesterol & Ca/uric acid | Baseline; optional for gout prophylaxis |
Tip: Keep a hydration log; fluid balance is key in managing diuretics.
Clinical Pearls
- “Lasix‑Start” Rule: When initiating IV Lasix, provide a 500‑1000 mL isotonic saline load to prevent hypotension and preserve renal perfusion.
- “Potassium‑Hygiene”: Supplement K⁺ (10–20 mmol) for every 500 mL of urine output > 100 mL to counteract diuretic‑induced losses.
- Vitamin C Synergy: In patients on high‑dose vitamin C, give daily oral Lasix 20 mg to reduce urinary oxalate excretion and prevent stones.
- Brand vs. Generic: Lasix and furosemide are bioequivalent; generic dosing guidelines apply universally.
- Renal Protection: For chronic loop use, co‑administer angiotensin‑converting enzyme inhibitors or angiotensin receptor blockers to slow GFR decline.
- Ototoxicity Prevention: Avoid paracetamol + Lasix + NSAIDs combo at high doses; if needed, monitor hearing and adjust dose.
- Sweet Tooth: Crystalluria risk increases with high oral doses; recommend a low‑sugar diet to minimize uric acid precipitation.
These concise yet comprehensive points provide medical students and clinicians with essential, up‑to‑date information about Lasix—from mechanism to monitoring—ensuring effective, safe patient care.