Adult: In cases associated with CHF or renal diseases (e.g. nephrotic syndrome, impaired renal function): As formulation with slow and incomplete absorption: Usual dose: 5-10 mg once daily, may be increased to 20 mg once daily if necessary. Dose must be individualised according to patient needs and response. Dosage recommendations may vary between individual products (refer to specific product guidelines). Elderly: Lower initial doses may be necessary.
Oral Hypertension
Adult: Monotherapy or in combination with other antihypertensive agents: As formulation with slow and incomplete absorption: Usual dose: 2.5-5 mg once daily. Dose must be individualised according to patient needs and response. Dosage recommendations may vary between individual products (refer to specific product guidelines). Elderly: Lower initial doses may be necessary.
Administration
Metolazone May be taken with or without food.
Contraindications
Anuria, hepatic coma or pre-comatose conditions.
Special Precautions
Patient with prediabetes or diabetes mellitus, SLE, hyperuricaemia or gout, sulfonamide hypersensitivity, pre-existing electrolyte disturbances. Avoid use for the treatment of hypertension in patients with primary adrenal insufficiency (Addison's disease). Metolazone is available in different preparations that may not be interchangeable due to differences in bioavailability; refer to specific product guidelines for detailed information. Severe renal and hepatic impairment. Elderly. Pregnancy and lactation.
Adverse Reactions
Significant: Electrolyte disturbances (e.g. hypokalaemia, hyponatraemia, hypomagnesaemia, hypercalcaemia), immediate and delayed hypersensitivity reactions (e.g. urticaria, angioedema, toxic epidermal necrolysis, Stevens-Johnson syndrome), hypotension, orthostatic hypotension, azotaemia, hyperuricaemia, gout attacks; activation or exacerbation of SLE; may increase blood glucose level, which may cause hyperglycaemia and glycosuria. Blood and lymphatic system disorders: Leucopenia, agranulocytosis, aplastic or hypoplastic anaemia, thrombocytopenia, haemoconcentration. Cardiac disorders: Chest pain or discomfort, palpitations. Ear and labyrinth disorders: Vertigo. Eye disorders: Transient blurred vision. Gastrointestinal disorders: Nausea, vomiting, diarrhoea, constipation, abdominal pain, bloating, pancreatitis, epigastric distress, dry mouth. General disorders and administration site conditions: Fatigue, weakness, chills. Hepatobiliary disorders: Hepatitis, intrahepatic cholestatic jaundice. Investigations: Increased BUN and serum creatinine. Metabolism and nutrition disorders: Hypochloraemia, hypochloraemic alkalosis, anorexia. Musculoskeletal and connective tissue disorders: Muscle pain and cramps, joint pain. Nervous system disorders: Headache, dizziness, neuropathy, paraesthesia, drowsiness. Psychiatric disorders: Restlessness, psychotic depression. Reproductive system and breast disorders: Impotence. Skin and subcutaneous tissue disorders: Vasculitis, purpura, petechiae, rash, pruritus, skin necrosis, photosensitivity. Vascular disorders: Syncope, venous thrombosis.
Correct electrolyte imbalance before treatment initiation. Monitor fluid balance, serum electrolyte, uric acid, blood pressure (standing, sitting or supine), and renal function. Assess for signs of fluid or electrolyte imbalance, hypotension, and hypersensitivity reactions.
Overdosage
Symptoms: Orthostatic hypotension, dizziness, drowsiness, gastrointestinal irritation and hypermotility, syncope, haemoconcentration, haemodynamic changes, dehydration and electrolyte disturbances (mainly hyponatraemia), temporary elevation of BUN, lethargy of varying degree that may progress to coma. Management: Symptomatic and supportive treatment. Administer activated charcoal (1 g/kg) within the 1st hour of ingestion to reduce absorption. Establish adequate hydration and re-establish electrolyte balance. Monitor electrolyte changes and CV and renal function.
Drug Interactions
Increased risk of hypokalaemia with corticosteroids. May increase the orthostatic hypotensive effect with other antihypertensive agents, barbiturates and opioids. Concomitant use with furosemide may result in excessive fluid depletion or severe electrolyte disturbances. Reduced therapeutic effects with NSAIDs. May reduce antihypertensive effect with sympathomimetic agents. May reduce lithium clearance and increase the risk of lithium toxicity. May increase the occurrence of hypersensitivity reactions to allopurinol. Concomitant use with ciclosporin may lead to increased serum creatinine. May reduce the efficacy of methenamine and antidiabetic agents. May increase the serum concentration of calcium salts. May increase the risk of adverse effects or toxicity of cardiac glycosides. May enhance the neuromuscular blocking effects of curariform agents (e.g. tubocurarine).
Food Interaction
May increase the orthostatic hypotensive effect with alcohol.
Lab Interference
May result in false-negative aldosterone/renin ratio.
Action
Description: Mechanism of Action: Metolazone is a quinazoline-derivative diuretic and antihypertensive agent. It blocks sodium reabsorption in the ascending branch of the loop of Henle and the proximal tubules, leading to increased excretion of sodium and water, as well as potassium and hydrogen ions. Onset: Diuresis: Within 1 hour. Duration: Diuresis: ≥24 hours. Pharmacokinetics: Absorption: Rate and extent of absorption depend on drug formulation. Distribution: Crosses the placenta and enters breast milk. Volume of distribution: 113 L. Plasma protein binding: 15-33%. Excretion: Via urine (80-95% as unchanged drug). Elimination half-life: 8-14 hours.
Chemical Structure
Metolazone Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 4170, Metolazone. https://pubchem.ncbi.nlm.nih.gov/compound/Metolazone. Accessed Aug. 27, 2025.
C03BA08 - metolazone ; Belongs to the class of low-ceiling sulfonamide diuretics.
References
Brayfield A, Cadart C (eds). Metolazone. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 06/08/2025.Joint Formulary Committee. Metolazone. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 06/08/2025.Metolazone Tablet (Ingenus Pharmaceuticals LLC). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 06/08/2025.Metolazone. Gold Standard Drug Database in ClinicalKey [online]. Elsevier Inc. https://www.clinicalkey.com. Accessed 06/08/2025.Metolazone. UpToDate Lexidrug, AHFS DI (Adult and Pediatric) Online. American Society of Health-System Pharmacists, Inc. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 06/08/2025.Metolazone. UpToDate Lexidrug, Lexi-Drugs Multinational Online. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 06/08/2025.Xaqua 5 mg Tablets (Renascience Pharma Limited). MHRA. https://products.mhra.gov.uk. Accessed 06/08/2025.
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