triamterene (Rx)

1-10%

CHF

Edema

Hypotension

Dizziness

Fatigue

HA

Photosensitivity

Rash

Diarrhea

Nausea

Vomiting

Hyperuricemia

Nephrotoxicity

Frequency Not Defined

GI upset

Thrombocytopenia

Nephrolithiasis

Folic acid antagonism

Contraindications

Hypersensitivity to triamterene

Anuria, severe liver disease, renal failure

Hyperkalemia

Concomitant use with K+-sparing diuretic, or K supplementation

Cautions

Use caution in acid-base imbalance, electrolyte abnormalities, hyperuricemia or gout, liver disease, renal impairment, renal stones

Patients should be observed regularly for possible occurrence of blood dyscrasias, liver damage or other idiosyncratic reactions

Periodic BUN and serum potassium determinations should be made to check kidney function, especially in patients with suspected or confirmed renal insufficiency; particularly important to make serum potassium determinations in elderly or diabetic patients receiving drug; these patients should be observed carefully for possible serum potassium increases

Electrolyte imbalance often encountered in diseases such as congestive heart failure, renal disease or cirrhosis may be aggravated or caused independently by any effective diuretic agent including triamterene; use of full doses of a diuretic when salt intake is restricted can result in a low-salt syndrome

Triamterene can cause mild nitrogen retention, which is reversible upon withdrawal of drug and is seldom observed with intermittent (every-other-day) therapy

Therapy may cause a decreasing alkali reserve, with possibility of metabolic acidosis

By the very nature of their illness, cirrhotics with splenomegaly sometimes have marked variations in their blood; since triamterene is a weak folic acid antagonist, it may contribute to appearance of megaloblastosis in cases where folic acid stores have been depleted; periodic blood studies in these patients recommended; observe also for exacerbations of underlying liver disease

Triamterene has elevated uric acid, especially in persons predisposed to gouty arthritis

Triamterene reported in renal stones in association with other calculus components; drug should be used with caution in patients with histories of renal stones

Interferes with fluorescent assay of quinidine

Not recommended for pregnancy-induced HTN; use during pregnancy may increase risk of cardiovascular defects and oral cleft in child

Hyperkalemia

• Drug tends to conserve potassium rather than to promote excretion as do many diuretics and, occasionally, can cause increases in serum potassium which, in some instances, can result in hyperkalemia; in rare instances, hyperkalemia has been associated with cardiac irregularities
• If hyperkalemia present or suspected, obtain an electrocardiogram; if tECG shows no widening of QRS or arrhythmia in presence of hyperkalemia, it is usually sufficient to discontinue therapy and any potassium supplementation, and substitute a thiazide alone
• Sodium polystyrene sulfonate may be administered to enhance excretion of excess potassium; presence of a widened QRS complex or arrhythmia in association with hyperkalemia requires prompt additional therapy
• For tachyarrhythmia, infuse 44 mEq of sodium bicarbonate or 10 mL of 10% calcium gluconate or calcium chloride over several minutes; for asystole, bradycardia or A-V block transvenous pacing is also recommended
• Effect of calcium and sodium bicarbonate is transient and repeated administration may be required; when indicated by clinical situation, excess K+ may be removed by dialysis or oral or rectal administration of Kayexalate®. Infusion of glucose and insulin has also been used to treat hyperkalemia

Pregnancy Category: C

Lactation: Discontinue drug or nursing

Pregnancy Categories

A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

NA: Information not available.

Mechanism of Action

Direct effect on renal distal tubule to inhibit Na+ reabsorption

Inhibits Na/K-ATPase, decreases Ca++ , Mg++ and hydrogen excretion

Pharmacokinetics

Half-Life: 1.5-2.5 hr

Duration: 7-9 hr

Onset: Initial effect: 2-4 hr; Max effect: diuresis: several days, HTN: 2-3 months

Peak Plasma Time: 1.5-3 hr

Bioavailability: 30-70%

Protein Bound: 55-67%

Metabolism: Liver

Metabolites: hydroxytriamterene sulfate (active)

Excretion: urine 21%

Dialyzable: Yes (hemodialysis)