Pharmacology of Triamterene/Hydrochlorothiazide

Brand Names

• Triamterene/Hydrochlorothiazide is marketed as Dyazide and Maxzide.

Drug Classification

• It belongs to the Potassium Sparing/Thiazide Diuretic Combination class.

Dosing Information

• For Edema: Administer 37.5 mg/25 mg, 1-2 tablets/capsules once daily.
• For Hypertension: Start with 37.5 mg/25 mg, 1 tablet/capsule once daily; titrate to a maximum of 75 mg/50 mg as needed.

Mechanism of Action

• Triamterene works in the distal tubular lumen, impacting sodium exchange for potassium and hydrogen, leading to a mild diuresis independent of aldosterone.
• Hydrochlorothiazide increases sodium and chloride excretion by hindering reabsorption in the nephron, resulting in urine that is mildly concentrated.

Renal Dose Adjustment

• Renal dose adjustments are necessary for this medication.

Pharmacogenetics

• There are no known pharmacogenetic considerations for this drug combination.

Contraindications

• Contraindicated in patients with hypersensitivity to hydrochlorothiazide, sulfonamides, or triamterene.
• Avoid use with potassium supplements, potassium-containing salt substitutes, other potassium-sparing diuretics, or in patients with anuria, renal insufficiency, or hyperkalemia.

Boxed Warnings

• Notable risks include hyperkalemia and an increased risk of skin cancer.

Drug Interactions

• Interactions may occur with Aliskiren, ACE inhibitors, angiotensin-receptor blockers, other potassium-sparing diuretics, Eplerenone, potassium supplements, salt substitutes, calcium supplements, antidiabetic medications, and NSAIDs.

Common Adverse Reactions

• Side effects often include hypotension, dizziness, and headache.

Rare but Serious Adverse Reactions

• Serious side effects can involve cardiac arrhythmias, hepatitis, hyperkalemia, gout, pancreatitis, Stevens-Johnson syndrome, and decreased visual acuity.

Efficacy Monitoring Parameters

• Monitor for decreased blood pressure and reductions in edema as indicators of efficacy.

Toxicity Monitoring Parameters

• Regularly check serum and urine electrolytes (calcium, magnesium, potassium, sodium) and renal function (creatinine levels and urine output).
• Look for increased serum uric acid or blood glucose levels, and seek medical help for skin rash, jaundice, decreased urine output, or gout symptoms.