Thiazide-like diuretic Pregnancy: Diuretics are best avoided for the management of oedema or hypertension in pregnancy as their use may be associated with hypovolaemia, increased blood viscosity and reduced placental perfusion; there have been reports of foetal bone marrow depression, thrombocytopenia, and foetal and neonatal jaundice associated with the use of thiazide diuretics. Hypertension during pregnancy is listed as a contraindication (§4.3). Chlortalidone passes into breast milk — mothers taking chlortalidone should refrain from breast-feeding their infants.

Chlortalidone

Brand names: Hygroton

Chlortalidone is a long-acting thiazide-like diuretic used for hypertension, with strong outcome evidence as an antihypertensive.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Hypertension: recommended starting dose 25 mg/day, which is sufficient to produce the maximum hypotensive effect in most patients; if the decrease in blood pressure proves inadequate the dose can be increased to 50 mg/day

Route: Oral, preferably as a single daily dose at breakfast time

Frequency: Once daily

Max: Indication-dependent — in oedema doses should not exceed 50 mg/day; in severe stable chronic heart failure the dose may be increased up to 100-200 mg/day. No single absolute daily maximum is stated in the SPC

Source: eMC SPC for Hylaton 12.5mg Tablets (single-agent chlortalidone). The dosage should be individually titrated to give the lowest effective dose; this is particularly important in the elderly. If a further reduction in blood pressure is required beyond 50 mg/day, additional antihypertensive therapy may be added to the regimen. Stable, chronic heart failure (NYHA functional class II/III): recommended starting dose 25 to 50 mg/day, increased in severe cases up to 100-200 mg/day; the usual maintenance dose is the lowest effective dose, e.g. 25-50 mg/day either daily or every other day. If the response proves inadequate, digitalis or an ACE inhibitor, or both, may be added. Oedema of specific origin: identify the lowest effective dose by titration and administer over limited periods only — doses should not exceed 50 mg/day. Diabetes insipidus: initially 100 mg twice daily, reducing where possible to a daily maintenance dose of 50 mg. Elderly patients: the lowest effective dose is recommended; elimination is slower than in healthy young adults although absorption is the same, so a reduction in the recommended adult dosage may be needed, with close medical observation. §4.5 (interactions) was not included in this bundle.

Paediatric dose

Route: Oral

Frequency: Every 48 hours

Max: 1.7 mg/kg every 48 hours

SPC §4.2: 'The lowest effective dose should also be used in children. For example, an initial dose of 0.5 to 1 mg/kg/48hours and a maximum dose of 1.7 mg/kg/48hours have been used.' The initial dose is stated as a range, so no single per-kg figure is recorded here. Verify against a children's formulary.

Dose adjustments

Renal

The lowest effective dose is recommended for patients with mild renal insufficiency. Contraindicated in severe renal failure (creatinine clearance below 30 mL/min). Chlortalidone and the thiazide diuretics lose their diuretic effect when the creatinine clearance is below 30 mL/min. Use with caution in patients with severe renal disease — thiazides may precipitate azotaemia in such patients and the effects of repeated administration may be cumulative.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Known hypersensitivity to chlortalidone or any of the excipients; hypersensitivity to chlortalidone and other sulphonamide derivatives
Anuria
Severe hepatic or renal failure (creatinine clearance below 30 mL/min)
Refractory hypokalaemia, hyponatraemia and hypercalcaemia
Symptomatic hyperuricaemia (history of gout or uric acid calculi)
Hypertension during pregnancy
Untreated Addison's disease
Concomitant lithium therapy

Side effects

Very common (mainly at higher doses): hypokalaemia, hyperuricaemia and a rise in blood lipids
Common: hyponatraemia, hypomagnesaemia, hyperglycaemia; postural hypotension; dizziness; urticaria and other forms of skin rash; loss of appetite and minor gastrointestinal distress; impotence
Uncommon: gout. Rare: hypercalcaemia, glycosuria, worsening of diabetic metabolic state; very rare: hypochloraemic alkalosis
Rare: cardiac arrhythmias; paraesthesia and headache; mild nausea and vomiting, gastric pain, constipation and diarrhoea; very rare: pancreatitis
Rare: thrombocytopenia, leucopenia, agranulocytosis and eosinophilia; intrahepatic cholestasis or jaundice; photosensitisation; idiosyncratic pulmonary oedema; allergic interstitial nephritis. Frequency unknown: choroidal effusion (sulfonamide-type idiosyncratic reaction with visual field defect, transient myopia and acute angle-closure glaucoma — discontinue as rapidly as possible)

Interactions

Lithium — concomitant lithium therapy is contraindicated (stated in SPC §4.3; §4.5 was not retrieved in this bundle, so the full interaction profile has not been extracted)

Clinical monograph

How it works

It inhibits sodium-chloride reabsorption in the distal convoluted tubule, producing a sustained diuresis and lowering blood pressure partly through reduced vascular resistance.

Prescribing in practice

Monitor U&E for hypokalaemia and hyponatraemia, which can be clinically significant and develop gradually.
Metabolic effects include hyperglycaemia, hyperuricaemia with gout, and hypercalcaemia.
Use caution in significant renal or hepatic impairment, and review electrolytes more closely in the elderly.

Monitoring

Monitor renal function and electrolytes (especially potassium and sodium) before starting and periodically, and consider checking glucose and urate where relevant.

Counselling the patient

Take it in the morning to reduce night-time urination.
Report muscle cramps, marked weakness or confusion, which may indicate a salt imbalance, and mention any history of gout.

Evidence & guidelines

Guideline-recognised thiazide-like diuretic with robust antihypertensive outcome data (NICE NG136).

Reference: NICE NG136; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

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