TRIAMTERENE

Clinical safety rating: safe

Animal studies have demonstrated safety

How it works

Triamterene is a potassium-sparing diuretic that inhibits epithelial sodium channels (ENaC) in the distal convoluted tubule and collecting duct of the nephron, reducing sodium reabsorption and potassium excretion.

What the body does with it

Metabolism	Triamterene is metabolized in the liver via hydroxylation and conjugation, primarily by cytochrome P450 enzymes (CYP1A2 and CYP3A4). Its active metabolite is hydroxytriamterene sulfate.
Excretion	Approximately 50% of an oral dose is excreted unchanged in urine; about 20% is excreted as metabolites (mainly hydroxytriamterene sulfate conjugate) in urine; biliary/fecal excretion accounts for less than 10%.
Half-life	Terminal elimination half-life is approximately 1.5 to 2 hours. However, in patients with hepatic cirrhosis, half-life may be prolonged up to 4 hours; in renal impairment, half-life can extend significantly (up to 10 hours) due to reduced renal clearance.
Protein binding	Approximately 67% bound to plasma proteins, primarily albumin.
Volume of Distribution	2.5 to 3.0 L/kg, indicating extensive tissue distribution including binding to renal tubules.
Bioavailability	Oral: approximately 30-70% due to first-pass metabolism; bioavailability is variable and reduced in patients with hepatic impairment.
Onset of Action	Oral: diuresis begins within 2 to 4 hours after administration.
Duration of Action	Oral: diuretic effect lasts approximately 7 to 9 hours; antihypertensive effect may persist for 12 to 24 hours with chronic dosing.

Classification & Brands

Dosing & administration

100-300 mg orally once daily; maximum 300 mg/day.

Dosage form	CAPSULE
Renal impairment	GFR 30-50 mL/min: reduce dose by 50%; GFR <30 mL/min: contraindicated.
Liver impairment	No dosage adjustment recommended; use with caution in severe hepatic impairment.
Pediatric use	2-4 mg/kg/day orally in divided doses; maximum 300 mg/day.
Geriatric use	Start at 100 mg orally once daily; titrate based on renal function and electrolyte monitoring.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

ACE inhibitors and ARBs may increase risk of hyperkalemia Can cause hyperkalemia and kidney stones.

Breastfeeding	Unknown if excreted in human breast milk. M/P ratio not established. Potential for serious adverse effects in nursing infant (hyperkalemia, electrolyte disturbances). Consider alternative diuretics; avoid breastfeeding during therapy.
Teratogenic Risk	Pregnancy Category C. First trimester: Potential risk based on animal studies showing teratogenic effects (cleft palate, skeletal abnormalities) at high doses. Second and third trimesters: Risk of electrolyte imbalances (hyponatremia, hyperkalemia) in mother and fetus; may cause fetal thrombocytopenia. Avoid use during pregnancy unless benefit outweighs risk.

Warnings & precautions

■ FDA Black Box Warning

None

Side Effect Profile

Common Effects	edema
Serious Effects

Absolute Contraindications

Absolute: Anuria, acute or chronic renal insufficiency, severe hepatic disease, hyperkalemia, hypersensitivity to triamterene. Relative: Concomitant use with other potassium-sparing diuretics or ACE inhibitors/ARBs; diabetes mellitus; elderly patients.

Clinical Precautions

Precautions

Hyperkalemia risk, especially in patients with renal impairment, diabetes, or using other potassium-sparing agents or potassium supplements; monitor serum potassium regularly. May cause electrolyte imbalances (hyponatremia, hypomagnesemia). Caution in patients with hepatic cirrhosis due to risk of folate deficiency and megaloblastic anemia. May cause photosensitivity.

Clinical Tips & Counseling

Drug interactions

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