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K-sparing diuretic (ENaC blocker) Pregnancy: US label: reproduction studies in rats at doses as high as 20 times the maximum recommended human dose on a body-weight basis (6 times on body-surface area) showed no evidence of harm to the fetus. Because animal reproduction studies are not always predictive of human response, the drug should be used during pregnancy only if clearly needed. Triamterene has been shown to cross the placental barrier and appear in cord blood; use in pregnant women requires that anticipated benefits be weighed against possible hazards to the fetus. The routine use of diuretics in an otherwise healthy woman is inappropriate and exposes mother and fetus to unnecessary hazard. Nursing mothers: triamterene has not been studied in nursing mothers; it appears in animal milk and is likely present in human milk, and if use is deemed essential the patient should stop nursing.

Triamterene

Brand names: Dytac

Triamterene is a potassium-sparing diuretic used, often in combination with a thiazide or loop diuretic, to manage oedema while limiting potassium loss.

Adult dose

Dose: Oedema associated with congestive heart failure, cirrhosis of the liver and the nephrotic syndrome, steroid-induced oedema, idiopathic oedema and oedema due to secondary hyperaldosteronism (triamterene used alone): usual starting dose 100 mg twice daily after meals; titrate to the needs of the individual patient.
Route: Oral (capsule)
Frequency: Twice daily, after meals (starting dose when used alone).
Max: 300 mg/day (US label: the total daily dosage should not exceed 300 mg)
US label (triamterene capsules, 50 mg strength). Dosage should be titrated to the needs of the individual patient. When combined with another diuretic or antihypertensive agent, the total daily dosage of each agent should usually be lowered initially and then adjusted to the patient's needs. When triamterene is added to other diuretic therapy, or patients are switched to it from other diuretics, all potassium supplementation should be discontinued. May be used alone or with other diuretics, either for added diuretic effect or its potassium-sparing potential, and promotes increased diuresis when patients are resistant or only partially responsive to thiazides or other diuretics because of secondary hyperaldosteronism. To help avoid stomach upset take after meals; if a single daily dose is prescribed it may be preferable to take it in the morning. If a dose is missed, do not take more than the prescribed dose at the next dosing interval. Routine use of diuretics in an otherwise healthy pregnant woman is inappropriate (see pregnancy text). No UK SPC for triamterene as a single agent is listed on eMC — this dose is from US prescribing information (Triamterene Capsules USP, Bryant Ranch Prepack) and must be verified against UK practice.

Dose adjustments

Renal

No dose figure is given. Contraindicated in anuria and in severe or progressive kidney disease or dysfunction, with the possible exception of nephrosis. Hyperkalaemia is more likely in patients with renal impairment; periodic BUN and serum potassium determinations should be made, especially in suspected or confirmed renal insufficiency.

Hepatic

No dose figure is given. Contraindicated in severe hepatic disease. Cirrhotics with splenomegaly may show marked variations in their blood: periodic blood studies are recommended and patients should be observed for exacerbations of underlying liver disease.

Dose independently re-sourced from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Anuria
  • Severe or progressive kidney disease or dysfunction, with the possible exception of nephrosis
  • Severe hepatic disease
  • Hypersensitivity to the drug or any of its components
  • Pre-existing elevated serum potassium (as sometimes seen in impaired renal function or azotaemia), or development of hyperkalaemia while on the drug
  • Concomitant dietary potassium supplements, potassium salts or potassium-containing salt substitutes
  • Other potassium-sparing agents such as spironolactone, amiloride hydrochloride, or other formulations containing triamterene (two deaths reported with concomitant spironolactone and triamterene)

Side effects

  • All adverse effects occur rarely (1 in 1000, or less)
  • Hypersensitivity: anaphylaxis, rash, photosensitivity
  • Metabolic: hyperkalaemia, hypokalaemia
  • Renal: azotaemia, elevated BUN and creatinine, renal stones, acute interstitial nephritis (rare), acute renal failure (one case of irreversible renal failure reported)
  • Gastrointestinal: jaundice and/or liver enzyme abnormalities, nausea and vomiting, diarrhoea
  • Haematologic: thrombocytopenia, megaloblastic anaemia (triamterene is a weak folic acid antagonist)
  • Central nervous system: weakness, fatigue, dizziness, headache, dry mouth
  • May cause mild nitrogen retention, a decreasing alkali reserve with the possibility of metabolic acidosis, and elevated uric acid in persons predisposed to gouty arthritis; reported in renal stones - use with caution in patients with a history of renal stones

Interactions

  • Potassium-sparing agents with ACE inhibitors - increased risk of hyperkalaemia; use with caution
  • Potassium-containing agents (blood from blood bank, low-salt milk, potassium-containing medications such as parenteral penicillin G potassium, salt substitutes) may promote serum potassium accumulation and hyperkalaemia, especially in renal insufficiency
  • Lithium - diuretic-induced sodium loss may reduce renal clearance of lithium and increase serum lithium levels with risk of lithium toxicity; monitor lithium levels closely and adjust the lithium dose if necessary
  • Indomethacin and other NSAIDs - possible interaction resulting in acute renal failure reported with indomethacin; caution advised
  • Effects potentiated: antihypertensive medication, other diuretics, preanaesthetic and anaesthetic agents, non-depolarising skeletal muscle relaxants
  • Triamterene may raise blood glucose levels - hypoglycaemic agent dosage adjustment may be necessary in adult-onset diabetes; concurrent use with chlorpropamide may increase the risk of severe hyponatraemia
  • Triamterene and quinidine have similar fluorescence spectra - triamterene will interfere with the fluorescent measurement of quinidine

Monitoring

  • Serum potassium at frequent intervals (abnormal elevation of 5.5 mEq/liter or greater can occur), especially when dosages are changed or with any illness that may influence renal function; particularly important in elderly or diabetic patients
  • Periodic BUN and serum potassium determinations to check kidney function, especially in suspected or confirmed renal insufficiency
  • If hyperkalaemia is present or suspected, obtain an electrocardiogram
  • Regular observation for blood dyscrasias, liver damage or other idiosyncratic reactions
  • Periodic blood studies in cirrhotic patients with splenomegaly, and observation for exacerbation of underlying liver disease
  • Electrolyte imbalance may be aggravated or caused by any effective diuretic; full doses of a diuretic with restricted salt intake can result in a low-salt syndrome
  • On prolonged or intensive therapy, withdrawal should be gradual because of the theorised possibility of rebound kaliuresis

Clinical monograph

How it works

It blocks epithelial sodium channels in the distal nephron, promoting sodium and water excretion while reducing potassium and hydrogen ion loss.

Prescribing in practice

  • It can cause hyperkalaemia, especially in renal impairment or when combined with ACE inhibitors, angiotensin receptor blockers, potassium supplements or other potassium-sparing drugs.
  • Avoid in significant renal impairment and in pre-existing hyperkalaemia.
  • It may cause a harmless blue discolouration of the urine and rarely contributes to renal stones.

Monitoring

Monitor serum potassium and renal function, particularly in older patients and those on interacting drugs.

Counselling the patient

  • Avoid potassium-containing salt substitutes unless advised otherwise.
  • Report muscle weakness, palpitations or numbness, which can indicate high potassium.
  • Your urine may appear bluish, which is harmless.

Evidence & guidelines

Potassium-sparing diuretics are used to offset potassium loss from thiazide or loop diuretics in line with established practice.

Reference: NICE; 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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