Triamterene and Hydrochlorothiazide

Triamterene and hydrochlorothiazide is a combination diuretic approved for two main conditions:

• High blood pressure (hypertension) — specifically for people who develop low potassium (hypokalemia) on hydrochlorothiazide alone, or who need a thiazide diuretic and cannot safely develop low potassium (for example, those on digitalis or with a history of irregular heartbeat)
• Edema (fluid retention) — for the same groups above; it is not intended as a first-line treatment for edema or hypertension in the general population
• It may be used alone or alongside other blood pressure medications such as beta-blockers — doses of those other drugs may need adjustment
• In pregnancy, diuretics are only appropriate when edema has a confirmed medical (pathological) cause, not for routine pregnancy-related swelling

Hydrochlorothiazide works in the kidneys by blocking the reabsorption of sodium and chloride, which causes more water to be excreted as urine. This reduces fluid in the body and helps lower blood pressure. However, this process also causes the kidneys to lose potassium. Triamterene works at a different point in the kidney to block sodium reabsorption while holding onto potassium — it essentially preserves the potassium that hydrochlorothiazide would otherwise flush out. Together, they produce a diuretic effect with a more balanced impact on potassium levels.

Triamterene does not work by blocking aldosterone (a hormone that regulates sodium and potassium) directly — it acts independently, so its effect does not depend on aldosterone levels. The antihypertensive (blood pressure–lowering) effect is driven primarily by the hydrochlorothiazide component.

Both forms are taken by mouth, generally once a day. The capsule form is usually one or two capsules taken as a single daily dose. The tablet form is also typically taken once daily as a single dose — dividing it into multiple smaller doses throughout the day is associated with a higher risk of electrolyte and kidney problems.

• Capsule: Taking it with a high-fat meal significantly increases the amount absorbed — take it consistently (always with food or always without) as directed by your prescriber
• Tablet: Take as a single daily dose; do not split into multiple daily doses unless specifically instructed
• If you miss a dose, follow your prescriber's or pharmacist's guidance — do not double up
• Your potassium levels will need to be checked regularly, especially at the start of therapy or after any dose change

Like all medications, this combination can cause side effects. Common ones include:

• Nausea, vomiting, stomach upset, diarrhea, or constipation
• Dizziness, headache, or fatigue
• Muscle cramps or weakness
• Increased sensitivity to sunlight
• Discolored urine
• Dry mouth or altered taste
• Dizziness when standing up quickly (orthostatic hypotension) — worse with alcohol

More serious reactions — including signs of high potassium (tingling, muscle paralysis, slow heartbeat), sudden eye pain or vision changes, jaundice (yellowing of the skin or eyes), or severe allergic reactions — require immediate medical attention. Long-term use of hydrochlorothiazide has been linked to a small increased risk of squamous cell skin cancer, especially in white patients; protect your skin from sun exposure and attend regular skin screenings.

• High potassium (hyperkalemia): The most critical risk — can be fatal if untreated. Most likely in people with kidney impairment, diabetes, older adults, and severely ill patients. Regular potassium blood tests are essential, especially at the start of treatment or when doses change.
• Kidney impairment: This medication is contraindicated (must not be used) in people with significant kidney problems or no urine output. Even mild kidney impairment requires close monitoring.
• Diabetes: High potassium can occur in diabetic patients even without kidney disease. Use with caution and monitor electrolytes frequently.
• Acute angle-closure glaucoma: A rare but serious eye reaction from the hydrochlorothiazide component. Symptoms — sudden eye pain, blurred vision — typically appear within hours to weeks of starting. Stop the medication and seek immediate medical care.
• Metabolic acidosis: Severely ill patients are at higher risk for potassium accumulation if acid-base balance is disrupted.
• Non-melanoma skin cancer: Long-term hydrochlorothiazide use has been associated with a small increase in squamous cell carcinoma risk, particularly in white patients taking large cumulative doses. Use sun protection and get regular skin checks.

This medication interacts with several drugs, supplements, and foods — always share your full medication list with your prescriber and pharmacist:

• ACE inhibitors (e.g., lisinopril, enalapril) — both raise potassium levels, increasing hyperkalemia risk
• Other potassium-sparing diuretics (spironolactone, amiloride) or other triamterene products — dangerous potassium accumulation
• Lithium — diuretics slow lithium clearance from the kidneys, raising the risk of lithium toxicity
• NSAIDs (e.g., ibuprofen, indomethacin) — possible risk of acute kidney failure
• Potassium supplements or potassium-containing salt substitutes — can cause a rapid, dangerous spike in potassium
• Chlorpropamide (older diabetes medication) — increased risk of severe low sodium
• Blood thinners (anticoagulants) — hydrochlorothiazide may reduce their effectiveness; dose adjustment may be needed
• Alcohol, barbiturates, or opioids — can worsen low blood pressure and dizziness, especially when standing
• Antigout medications — this combination can raise uric acid levels, possibly requiring dose adjustment of gout medications

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Kidney disease or no urine output: Do not use if you have significant kidney impairment or anuria — this medication is contraindicated
• High potassium (hyperkalemia): Do not use if your potassium is already elevated
• Diabetes: Use with caution; hyperkalemia can occur even without kidney disease — potassium monitoring is essential
• Older adults: Higher risk of potassium buildup and drug accumulation — requires frequent monitoring
• Sulfonamide or penicillin allergy: May increase risk of the rare eye reaction (acute angle-closure glaucoma) caused by the sulfonamide component
• Pregnancy: Routine diuretic use in pregnancy is not recommended. Use is appropriate only when edema has a confirmed pathological cause, not for normal pregnancy-related swelling
• Severely ill patients: At increased risk of acid-base imbalances and elevated potassium — use with extra caution
• Tell your doctor about all other medications, including over-the-counter NSAIDs, potassium supplements, salt substitutes, lithium, or ACE inhibitors

There is no specific antidote for a triamterene and hydrochlorothiazide overdose. Too much of the triamterene component may cause high potassium, dehydration, nausea, vomiting, weakness, and low blood pressure. Too much hydrochlorothiazide may cause low potassium, low sodium, dehydration, and in severe cases, confusion progressing to coma. If an overdose is suspected, seek emergency medical care immediately — treatment focuses on correcting fluid and electrolyte imbalances and providing supportive care.

Hydrochlorothiazide increases urine output by blocking sodium and chloride reabsorption in the kidneys, which also leads to water excretion and lowers blood volume and blood pressure. It reduces calcium excretion but may increase uric acid levels. Triamterene independently reduces sodium reabsorption at a different kidney site, which conserves potassium and hydrogen ions that would otherwise be lost. Together, the two components produce diuresis (increased urine output) while partially offsetting each other's effects on potassium.

After an oral dose of the capsule form, diuresis begins within about 1 hour, peaks at 2 to 3 hours, and tapers off over the following 7 to 9 hours. The medication is well absorbed, though taking the capsule with a high-fat meal can increase the absorption of triamterene by roughly 67% and delay absorption by up to 2 hours — so consistency with food intake matters. Triamterene is metabolized to an active compound (hydroxytriamterene sulfate), and both triamterene and hydrochlorothiazide are cleared more slowly in older adults and people with kidney impairment, which increases the risk of drug accumulation and side effects in those groups.

Store at controlled room temperature 20° to 25°C (68° to 77°F) . Protect from moisture. Protect from light.