Makindo Medical Notes

Always check the BNF here for up-to-date prescribing advice.

• Thiazide-like diuretic with potent natriuretic effect.
• Typically used in combination with loop diuretics in resistant oedema.
• Short-term use is common due to risk of profound electrolyte disturbance.

⚙️ Mode of Action

• Blocks sodium reabsorption at the distal convoluted tubule (DCT), enhancing excretion of sodium, chloride, and water.
• Causes increased delivery of sodium to the distal nephron, promoting potassium and hydrogen ion excretion.
• Very potent in combination with loop diuretics due to synergistic action.

📋 Indications / Dose

• Congestive Cardiac Failure (CCF): Metolazone 2.5 mg OD (short-term, specialist supervision).
• Used for refractory oedema where loop diuretics alone are insufficient.

🔄 Interactions

• Caution with other diuretics ➝ ↑ risk of hypokalaemia, hyponatraemia, dehydration.
• Monitor electrolytes, renal function, and BP/HR closely.
• May potentiate lithium toxicity (reduced clearance).

⚠️ Cautions

• Diabetes mellitus (may worsen glycaemic control).
• Gout (may precipitate flares due to hyperuricaemia).
• Nephrotic syndrome.
• Systemic lupus erythematosus (SLE).
• Close monitoring of electrolytes, renal function, and fluid balance essential.

⛔ Contraindications

• See BNF for full list.
• Severe renal or hepatic impairment.
• Hypokalaemia, hyponatraemia, or hypovolaemia.
• Hypersensitivity to thiazides/thiazide-like diuretics.

⚡ Side Effects

• Electrolyte disturbances: ⬇️ sodium, potassium, magnesium; ⬆️ calcium, glucose, urate.
• Volume depletion ➝ hypotension, AKI, over-diuresis.
• Gout flares (due to raised uric acid).
• Metabolic alkalosis (low Cl⁻/HCO₃⁻ changes).
• Haematological: ↓ WCC, granulocytes, platelets (rare).
• Skin: Rashes, photosensitivity.
• Hepatic: Rare cholestasis.
• Pulmonary: Rare pneumonitis.

📚 References

• BNF – Metolazone
• UpToDate – “Use of metolazone in diuretic-resistant oedema.”