Makindo Medical Notes

💧 Loop diuretics such as Bumetanide are potent agents used for rapid fluid removal in heart failure, renal, or hepatic oedema. They should not be used long-term for simple gravitational oedema — which usually improves with leg elevation, compression stockings, and increased ambulation. Always 🔗 check the BNF entry here for up-to-date prescribing guidance and safety advice.

🧬 Chemistry & Class

• Class: Loop diuretic (high-ceiling diuretic).
• Chemical name: 3-(butylamino)-4-phenoxy-5-sulfamoylbenzoic acid.
• Heavily bound to plasma albumin → secreted into the renal tubule via active transport.
• Approximately 40× more potent than furosemide by weight, but shorter-acting (half-life ≈ 1 hour).

⚙️ Mode of Action

• Inhibits the Na⁺/K⁺/2Cl⁻ cotransporter (NKCC2) in the thick ascending limb of the loop of Henle.
• Blocks sodium, chloride, and potassium reabsorption → increased urinary excretion of water and electrolytes.
• Also increases calcium and magnesium loss.
• Rapid onset of action: within 30 minutes orally and 5 minutes IV.
• Effectiveness depends on renal function and tubular secretion; may be diminished in renal impairment.

💊 Indications

• Acute left ventricular failure: 1–2 mg IV stat, may repeat or infuse if refractory.
• Congestive cardiac failure: 1 mg OD–2 mg BD PO (adjust to clinical response).
• Hypertension: 1 mg OD PO, usually in combination with ACE inhibitor or ARB (not used alone).
• Liver cirrhosis with ascites: 1 mg OD PO; combine with spironolactone for best control.
• Nephrotic syndrome: 1 mg OD PO, titrate according to response.
• Hypercalcaemia or hyperkalaemia (adjunct): IV loop diuretic with saline infusion to enhance electrolyte excretion.

📊 Dose Range (Always confirm with BNF or SPC)

🧠 Clinical Pearls

• Bumetanide is often used when there is poor gut absorption of furosemide (e.g. oedematous bowel in advanced HF).
• It produces a more predictable diuretic response than furosemide in some patients with renal impairment.
• Conversion: 1 mg bumetanide ≈ 40 mg furosemide (rough guide).
• Administer early in the day to avoid nocturia.
• In diuretic resistance, consider adding metolazone (synergistic distal action) but monitor electrolytes closely.

⚠️ Contraindications & Precautions

• Avoid with ototoxic drugs (e.g. aminoglycosides, cisplatin).
• Monitor renal function (U&E, eGFR) — risk of pre-renal AKI if over-diuresed.
• Hypokalaemia increases digoxin toxicity and predisposes to arrhythmias.
• Use cautiously in gout, diabetes, or severe liver disease.

💢 Side Effects

• Volume depletion → orthostatic hypotension, dizziness, syncope, falls (especially elderly).
• Electrolyte imbalance:
  • ↓K⁺ → arrhythmias, weakness.
  • ↓Mg²⁺ → arrhythmias, cramps.
  • ↓Ca²⁺ with ↑ urinary calcium excretion.
• Metabolic:
  • ↑Uric acid (gout), ↑Glucose (impaired tolerance), ↑Cholesterol.
• Ototoxicity (tinnitus, hearing loss) — more likely with high IV doses or concurrent ototoxins.

🤝 Interactions

• Digoxin: hypokalaemia increases toxicity risk.
• Lithium: reduced clearance → lithium accumulation and toxicity.
• NSAIDs: blunt diuretic and antihypertensive effect; may precipitate renal impairment.
• ACE inhibitors / ARBs: additive risk of hypotension and renal dysfunction.
• Ototoxic drugs: aminoglycosides, cisplatin → additive hearing risk.

🧮 Monitoring

• Baseline and follow-up U&E, creatinine, eGFR, bicarbonate.
• Monitor electrolytes daily if IV therapy, or weekly if stable outpatients.
• Check weight and fluid balance daily in hospital (aim ≤1 kg/day loss in HF).
• Monitor for symptomatic hypotension, cramps, dizziness, and tinnitus.

📚 References

• BNF: Bumetanide
• NICE NG106: Chronic heart failure in adults – management.
• Renal Association (2024): Diuretic therapy and monitoring in CKD.
• MHRA Drug Safety Update: Loop diuretics and ototoxicity (2022).