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Thiazide-Like Diuretic Pregnancy: Avoid unless essential — insufficient safety data

Metolazone

Brand names: Metenix (discontinued in UK), metolazone (imported/special)

Adult dose

Dose: 2.5–10 mg OD (intermittent dosing in specialist setting — typically 3 times/week or as needed for resistant oedema)
Route: Oral
Frequency: Once daily or intermittent (specialist guided)
Max: 20 mg OD (rarely used; under specialist supervision)
Unlicensed in UK (imported). Used as add-on to loop diuretic for resistant oedema — 'sequential nephron blockade'. Potent — can cause profound diuresis and electrolyte disturbances. Initiate under close supervision.

Paediatric dose

Dose: 0.1 mg/kg
Route: Oral
Frequency: OD
Max: 10 mg OD
Off-label paediatric use; doses 0.1–0.2 mg/kg OD under specialist supervision for resistant oedema

Dose adjustments

Renal

Effect may be reduced in renal impairment but still works at lower eGFR (unlike other thiazides — metolazone retains activity at eGFR <30)

Hepatic

Caution — may precipitate hepatic encephalopathy

Paediatric weight-based calculator

Off-label paediatric use; doses 0.1–0.2 mg/kg OD under specialist supervision for resistant oedema

Clinical pearls

  • Unique property: remains effective even when eGFR is very low (unlike other thiazides) — hence use in CKD
  • Sequential nephron blockade (metolazone + furosemide): can produce diuresis even in severe diuretic resistance
  • Must be initiated as inpatient or very closely monitored — profound electrolyte disturbances and hypovolaemia can occur within hours
  • UK-unlicensed — obtained as named patient special import; document clinical justification

Contraindications

  • Anuria
  • Pre-coma/coma in hepatic failure
  • Hypersensitivity to sulfonamides

Side effects

  • Profound hypokalaemia
  • Hyponatraemia
  • Hypomagnesaemia
  • Volume depletion
  • Hyperuricaemia
  • Hyperglycaemia

Interactions

  • Loop diuretics — dramatic synergistic diuresis (sequential nephron blockade)
  • NSAIDs — reduced diuretic effect
  • ACEi/ARBs — enhanced hypotension and renal impairment
  • Digoxin — hypokalaemia increases toxicity

Monitoring

  • Serum electrolytes (Na+, K+, Mg2+) — daily if started as inpatient
  • Urine output and weight
  • Renal function
  • Blood pressure

Reference: BNFc; BNF; ESC Heart Failure Guidelines 2021; AHA/ACC HF Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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