Pharmacologic classification: potassium-sparing diuretic
Therapeutic classification: diuretic
Pregnancy risk category B

Available forms
Available by prescription only
Capsules: 50 mg, 100 mg

Indications and dosages
 Edema. Adults: Initially, 100 mg P.O. b.i.d. after meals. Total daily dose shouldn’t exceed 300 mg.

Diuretic action: Triamterene acts directly on the distal renal tubules to inhibit sodium reabsorption and potassium excretion, reducing potassium loss.
Triamterene is commonly used with other more effective diuretics to treat edema related to excessive aldosterone secretion, hepatic cirrhosis, nephrotic syndrome, and heart failure.

Absorption: Absorbed rapidly after oral administration, but the extent varies. Diuretic effect may be delayed 2 to 3 days if used alone; maximum antihypertensive effect may be delayed 2 to 3 weeks.
Distribution: About 67% protein-bound.
Metabolism: Metabolized by hydroxylation and sulfation.
Excretion: Excreted in urine; half-life of triamterene is 100 to 150 minutes.

Route Onset Peak Duration
P.O. 2-4 hr 6-8 hr 12-16 hr

Contraindications and precautions
Contraindicated in patients receiving other potassium-sparing drugs, such as spirolactone or amiloride hydrochloride; in those hypersensitive to drug; and in patients with anuria, severe or progressive renal disease or dysfunction, severe hepatic disease, or hyperkalemia.
  Use cautiously in patients with impaired hepatic function or diabetes mellitus and in geriatric or debilitated patients.

Drug-drug. ACE inhibitors, such as captopril and enalapril; potassium-containing drugs, such as parenteral penicillin G; potassium-sparing diuretics; potassium supplements: Increases risk of hyperkalemia. Monitor patient closely.
Antihypertensives: Enhances hypoglycemia. Monitor patient closely. May be a therapeutic advantage.
Cimetidine: Increases bioavailability of triamterene. Monitor patient closely.
Lithium: Decreases lithium clearance. Avoid use together.
NSAIDs: Alters potassium excretion. Monitor patient closely.
Drug-herb. Licorice root: May contribute to potassium depletion caused by thiazides. Discourage use together.
Drug-food. Potassium-containing salt substitutes, potassium-rich foods: Increases risk of hyperkalemia. Discourage use together.
Drug-lifestyle. Sun exposure: May cause photosensitivity reactions. Advise patient to take precautions.

Adverse reactions
CNS: dizziness, weakness, fatigue, headache.
CV: hypotension.
GI: dry mouth, nausea, vomiting, diarrhea.
GU: interstitial nephritis.
Hematologic: megaloblastic anemia related to low folic acid levels, agranulocytosis, thrombocytopenia.
Hepatic: jaundice.
Metabolic: hyperkalemia, acidosis, hypokalemia, azotemia.
Musculoskeletal: muscle cramps.
Skin: photosensitivity, rash.
Other: anaphylaxis.

Effects on lab test results
• May increase BUN, creatinine, glucose, and uric acid levels. May decrease sodium levels. May increase or decrease potassium levels.
• May increase liver function test values. May decrease hemoglobin and granulocyte and platelet counts.

Overdose and treatment
Signs and symptoms of overdose include those indicative of dehydration and electrolyte disturbance.
 Treatment is supportive and symptomatic. For recent ingestion (less than 4 hours), empty stomach by induced emesis or gastric lavage. In severe hyperkalemia (more than 6.5 mEq/L), reduce serum potassium levels with I.V. sodium bicarbonate or glucose with insulin. A cation exchange resin, sodium polystyrene sulfonate (Kayexalate), given orally or as a retention enema, may also reduce serum potassium levels. Hemodialysis may have some benefit.

Special considerations
• Drug is less potent than thiazides and loop diuretics and is useful as an adjunct to other diuretic therapy. Usually used with potassium-wasting diuretics. Full effect is delayed 2 to 3 days when used alone.
• To minimize excessive rebound potassium excretion, withdraw drug gradually.
• Monitor blood pressure, CBC, and blood uric acid, blood glucose, BUN, and serum electrolyte levels.
• Watch for blood dyscrasia.
Pregnant patients
• Use drug during pregnancy only when potential benefits justify possible risk to fetus.
Breast-feeding patients
• Drug may appear in breast milk. Safety during breast-feeding hasn’t been established.
Pediatric patients
• Use cautiously; children are more susceptible to hyperkalemia.
Geriatric patients
• Elderly and debilitated patients need close observation because they’re more susceptible to drug-induced diuresis and hyperkalemia. Reduced doses may be indicated.

Patient education
• To prevent serious hyperkalemia, warn patient to avoid excessive ingestion of potassium-rich foods, such as citrus fruits, tomatoes, bananas, dates, and apricots; potassium-containing salt substitutes; and potassium supplements.
• Advise patient to avoid direct sunlight, wear protective clothing, and use a sunblock to prevent photosensitivity reactions.
• Tell patient his urine may turn blue.
• Tell patient to promptly report weakness, sore throat, headache, fever, bruising, bleeding, mouth sores, nausea, vomiting, and dry mouth.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use