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K-sparing + thiazide-like diuretic Pregnancy: Thiazide diuretics have been shown to cross the placenta and also to appear in breast milk. In rare instances, thrombocytopenia, pancreatitis or hypokalaemia have been reported in newborn infants of mothers treated with thiazide diuretics. The use of this medicine in pregnant or nursing mothers should therefore be avoided unless essential. (SPC 4.6)

Triamterene with chlortalidone

A fixed-dose combination of triamterene (a potassium-sparing diuretic) with chlortalidone (a thiazide-like diuretic), used for hypertension and oedema while limiting potassium loss.

Adult dose

Dose: Mild to moderate hypertension: usually one tablet (triamterene 50 mg / chlortalidone 50 mg) daily taken after breakfast; if necessary the dose may be increased to two tablets taken once daily. Oedema (congestive cardiac failure, nephrosis, corticosteroid or oestrogen therapy): the usual dose is one tablet daily taken after breakfast; if oedema persists after seven to ten days the dose may be increased to two tablets daily.
Route: Oral (tablets, each triamterene 50 mg / chlortalidone 50 mg)
Frequency: Once daily, after breakfast
Product: UK SPC via MHRA Products - TRIAMTERENE/CHLORTALIDONE 50MG/50MG FILM-COATED TABLETS (PL001110003), DHP Healthcare Limited. SPC 2: 'Chlortalidone BP 50mg Triamterene BP 50mg' (per tablet). SPC 4.1 verbatim: 'i) Management of mild to moderate hypertension. ii) Oedema associated with congestive cardiac failure, nephrosis, corticosteroid or oestrogen therapy. iii) Ascites associated with hepatic cirrhosis.' SPC 4.2 verbatim: 'Hypertension: Usually one tablet daily taken after breakfast. If necessary the dose may be increased to two tablets taken once daily. Oedema: The usual dose is one tablet daily taken after breakfast. If oedema persists after seven to ten days the dose may be increased to two tablets daily. Dosage in children has not been established and this medicine is recommended for the treatment of adults only. The elderly may require a lower dosage schedule.' The SPC prints no separate maximum dose (two tablets daily is the highest regimen printed) and no separate regimen for ascites associated with hepatic cirrhosis (indication iii).

Dose adjustments

Renal

No dose-reduction schedule is printed. Progressive renal failure is a contraindication (SPC 4.3); caution in severe kidney disease (SPC 4.4); if progressive renal impairment becomes evident, withdraw and institute alternative therapy if necessary (SPC 4.4). The elderly may require a lower dosage schedule (SPC 4.2).

Hepatic

No dose-reduction schedule is printed. SPC 4.4: caution should be exercised in patients with impaired liver function or progressive liver disease.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via MHRA Products — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the individual components or to other sulphonamide-derived drugs (SPC 4.3)
  • Progressive renal failure (SPC 4.3)
  • Concomitant lithium therapy (SPC 4.3)
  • Hyperkalaemia (plasma potassium above 5.0 mmol/litre) (SPC 4.3)
  • Patients receiving other potassium-sparing agents such as spironolactone or amiloride (SPC 4.3)

Side effects

  • Similar to thiazide therapy: nausea, dry mouth, constipation, leg cramp, headaches, dizziness and fatigue (SPC 4.8)
  • Choroidal effusion with visual field defect - frequency not known; acute myopia and secondary angle-closure glaucoma (SPC 4.4)
  • Megaloblastic anaemia - rare cases in association with triamterene (SPC 4.8)
  • Hyperkalaemia - signs include paraesthesia, muscular weakness, fatigue, flaccid paralysis of the extremities, bradycardia, shock and ECG abnormalities (SPC 4.4)
  • Hyperuricaemia or precipitation of acute gout; chlortalidone has occasionally aggravated or precipitated diabetes mellitus; triamterene may cause a decreasing alkali reserve with the possibility of metabolic acidosis (SPC 4.4)

Interactions

  • May add to or potentiate the action of other antihypertensive drugs (SPC 4.5)
  • Orthostatic hypotension may be aggravated by concomitant alcohol, barbiturates or narcotics (SPC 4.5)
  • Chlortalidone and related drugs may increase the responsiveness to tubocurarine (SPC 4.5)
  • Lithium: contraindicated (SPC 4.3)
  • Other potassium-sparing agents (spironolactone, amiloride): contraindicated; potassium supplements should not be given except in the presence of hypokalaemia (SPC 4.3/4.4)

Monitoring

  • Plasma potassium at the time of dosage adjustments and at appropriate intervals during therapy, particularly in elderly or diabetic patients with confirmed or suspected renal insufficiency (SPC 4.4)
  • If hyperkalaemia occurs, withdraw the product, substitute a diuretic and restrict potassium intake; if plasma potassium exceeds 6.5 mmol per litre active measures should be taken to reduce it (SPC 4.4)
  • Hyperuricaemia / acute gout and glycaemic control in diabetes (SPC 4.4)
  • Acute onset of decreased visual acuity or ocular pain (possible angle-closure glaucoma) - discontinue as rapidly as possible (SPC 4.4)

Clinical monograph

How it works

Chlortalidone inhibits the distal tubular sodium-chloride co-transporter to produce sustained natriuresis, while triamterene blocks distal epithelial sodium channels to reduce potassium excretion, balancing the potassium-losing effect of the thiazide-like component.

Prescribing in practice

  • The triamterene component risks hyperkalaemia, which is amplified by renal impairment and by concomitant ACE inhibitors, ARBs, potassium supplements or potassium-sparing agents, so these combinations need care.
  • Chlortalidone has a long duration of action and can cause hypokalaemia, hyponatraemia, hyperuricaemia and impaired glucose tolerance, so the two components are balanced but still require electrolyte vigilance.
  • It is contraindicated in significant renal impairment, anuria and pre-existing hyperkalaemia.

Monitoring

Monitor serum potassium, sodium and renal function before starting and periodically thereafter, especially in older patients or those on interacting drugs.

Counselling the patient

  • Avoid potassium-containing salt substitutes unless advised.
  • Report muscle weakness, palpitations, cramps or confusion.
  • Keep up with the blood tests for your kidneys and potassium.

Evidence & guidelines

Combining a potassium-sparing diuretic with a thiazide-like agent to offset potassium loss is a long-established approach, and chlortalidone has robust outcome data for blood-pressure lowering in hypertension.

Reference: 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).

Related

Curated clinical cross-links plus same-class fallbacks.

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