What is the recommended adult dosing and titration of the fixed‑combination triamterene 37.5 mg/hydrochlorothiazide 25 mg tablet, and what monitoring is needed?

Triamterene-HCTZ 37.5-25 MG Tablet Dosing

Standard Adult Dosing

The recommended adult dose is one tablet (triamterene 37.5 mg/hydrochlorothiazide 25 mg) once daily, taken in the morning with food to minimize gastrointestinal upset. 1

• This fixed-dose combination provides potassium-sparing diuretic effect while maintaining antihypertensive efficacy 1
• The formulation delivers optimal bioavailability when taken as a single morning dose 2
• Taking with food enhances absorption and reduces gastric irritation 2

Titration and Dose Adjustment

• Do not exceed one tablet daily – higher doses markedly increase hyperkalemia risk without proportional blood pressure benefit 1
• If blood pressure remains uncontrolled after 2-4 weeks on one tablet daily, add a second antihypertensive agent (such as an ACE inhibitor or calcium channel blocker) rather than increasing the diuretic dose 1
• For patients switching from separate hydrochlorothiazide and triamterene tablets, one combination tablet provides equivalent or superior bioavailability to the individual components 2, 3

Critical Monitoring Requirements

Initial Phase (First 2 Weeks)

• Check serum potassium and creatinine within 5-7 days of initiation – this is the highest-risk period for hyperkalemia 4
• Repeat potassium and creatinine at 2 weeks 4
• Monitor blood pressure weekly until target is achieved 1

Maintenance Phase

• Check potassium and renal function at 1 month, 3 months, then every 3-6 months thereafter 4
• Hold the medication immediately if potassium rises above 5.5 mEq/L and recheck within 48-72 hours 4
• Discontinue permanently if potassium exceeds 6.0 mEq/L 4

High-Risk Populations Requiring Intensive Monitoring

• Chronic kidney disease (eGFR <60 mL/min) – check potassium every 5-7 days until stable, then weekly for first month 4
• Diabetes mellitus – monitor potassium twice weekly for first 2 weeks due to impaired renal potassium handling 4
• Concurrent ACE inhibitor or ARB therapy – this combination dramatically increases hyperkalemia risk and requires potassium checks every 5-7 days initially 4
• Age ≥75 years – start monitoring at 3-5 days post-initiation due to reduced renal reserve 1

Absolute Contraindications

• Serum potassium >5.0 mEq/L at baseline – do not initiate therapy 4
• eGFR <30 mL/min or creatinine >1.8 mg/dL – severe hyperkalemia risk 1, 4
• Concurrent potassium supplementation – never combine with oral potassium chloride or potassium-containing salt substitutes 4
• Concurrent use with other potassium-sparing diuretics (spironolactone, amiloride, eplerenone) – causes life-threatening hyperkalemia 4
• Pregnancy – causes fetal harm; discontinue immediately if pregnancy detected 1

Critical Drug Interactions

• NSAIDs (including ibuprofen, naproxen) – absolutely contraindicated; cause acute renal failure and severe hyperkalemia when combined with triamterene 4
• ACE inhibitors/ARBs – if combination is necessary, reduce or discontinue any existing potassium supplementation and monitor potassium every 5-7 days 4
• Aldosterone antagonists – never combine; this is a Class III (Harm) recommendation 4
• Lithium – triamterene reduces lithium clearance; monitor lithium levels closely 1

Special Clinical Situations

Switching from Dyazide (50-25 mg capsules)

• One Maxzide tablet (37.5-25 mg) delivers approximately twice the bioavailable hydrochlorothiazide as one Dyazide capsule due to superior absorption 2
• When converting from two Dyazide capsules daily to one triamterene-HCTZ 37.5-25 mg tablet, expect improved blood pressure control 2
• Monitor for hypotension in the first week after switching 2

Hepatic Impairment

• Use with extreme caution in cirrhosis – triamterene can precipitate hepatic encephalopathy 1
• Monitor electrolytes every 3-5 days in patients with ascites 1

Heart Failure

• Target serum potassium 4.0-5.0 mEq/L in heart failure patients, as both hypokalemia and hyperkalemia increase mortality 4
• If patient is on ACE inhibitor or ARB for heart failure, strongly consider using hydrochlorothiazide alone rather than the combination to avoid hyperkalemia 4

Common Pitfalls to Avoid

• Never supplement potassium while on triamterene-HCTZ – this is the most common cause of severe hyperkalemia in clinical practice 4
• Do not assume "potassium-sparing" means potassium supplementation is safe – the opposite is true 4
• Avoid combining with ACE inhibitors/ARBs without specialist consultation in patients with diabetes or CKD 4
• Do not continue therapy if creatinine rises >50% from baseline – this signals acute kidney injury requiring immediate discontinuation 4
• Never use in patients already taking spironolactone – this combination causes predictable, severe hyperkalemia 4

Target Blood Pressure Goals

• Aim for <130/80 mmHg in most adults with hypertension 1
• Reassess blood pressure every 2-4 weeks during titration 1
• If target not achieved after 4-8 weeks on one tablet daily, add a second agent from a different class rather than increasing diuretic dose 1

Patient Counseling Points

• Take in the morning to avoid nocturia 1
• Avoid all potassium-containing salt substitutes (e.g., Nu-Salt, Morton Salt Substitute) – these can cause fatal hyperkalemia 4
• Limit high-potassium foods (bananas, oranges, potatoes, tomatoes) while on this medication 4
• Report muscle weakness, irregular heartbeat, or confusion immediately – these are signs of hyperkalemia 4
• Avoid NSAIDs entirely, including over-the-counter ibuprofen and naproxen 4