Mechanism of effect
Triamterene inhibits the epithelial sodium channels (ENaC) located on the lumenal side in the late distal convoluted tubule and collecting tubule, which are transmembrane channels that normally promotes sodium uptake and potassium secretion. In the late distal tubule to the collecting duct, sodium ions are actively reabsorbed via ENaC on the lumnial membrane and are extruded out of the cell into the peritubular medium by a sodium-potassium exchange pump, the Na-K-ATPase, with water following passively. Triamterene exerts a diuretic effect on the distal renal tubule to inhibit the reabsorption of sodium ions in exchange for potassium and hydrogen ions and its natriuretic activity is limited by the amount of sodium reaching its site of action. Its action is antagonistic to that of adrenal mineralocorticoids, such as aldosterone, but it is not an inhibitor or antagonist of aldosterone. Triamterene maintains or increases the sodium excretionm, thereby increasing the excretion of water, and reduces the excess loss of potassium, hydrogen and chloride ions by inhibiting the distal tubular exchange mechanism. Due to its diuretic effect, triamterene rapidly and reversibly reduces the lumen-negative transepithelial potential difference by almost complete abolition of Na+ conductance without altering K+ conductance. This reduces the driving force for potassium movement into the tubular lumen and thus decreases potassium excretion. Triamterene is similar in action to amiloride but, unlike amiloride, increases the urinary excretion of magnesium.
Pharmacodynamic
As triamterene tends to conserve potassium more strongly than promoting Na+ excretion, it can cause an increase in serum potassium, which may result in hyperkalemia potentially associated with cardiac irregularities. In healthy volunteers administered with oral triamterene, there was an increase in the renal clearnace of sodium and magnesium, and a decrease in the clearance of uric acid and creatinine due to its effect of reducing glomerular filtration renal plasma flow. Triamterene does not affect calcium 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)
Dosage
Adult
Edema
100-300 mg/day PO qDay or divided q12hr
Hypertension
100-300 mg/day PO qDay or divided q12hr
Pediatric
Hypertension (Off-label)
Safety & efficacy not established
1-2 mg/kg/day PO divided q12hr
Maximum dose: 3-4 mg/kg/day PO divided q12hr up to 300 mg/daySide effects
Diarrhea , Headache , edema , nausea , vomiting , vertigo , Photosensitivity , Congestive heart failure , tiredness , Rash , NephrotoxicityInteractions
Amlodipine/Atorvastatine , Drospirenone , Amiloride , potassium citrate , ethacrynic acid , novafen , Spironolactone , Tacrolimus , Losartan , Lisinopril , Valsartan , Captopril , Trandolapril , Perindopril , Benazepril , Moexipril , quinapril , eplerenone , Trimethoprim , lithium , sulfamethoxazole+trimethoprim , Fosinopril , Ramipril , Eprosartan , Canagliflozin , Telmisartan , Sacubitril and valsartan , Acemetacin , Azilsartan , Candesartan , Irbesartan , Olmesartan , TreprostinilAlerts
Acid-base imbalance, electrolyte abnormalities, hyperuricemia or gout, liver dz, renal impairment, renal stones
Breastfeeding
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
Points of recommendation
Take triamterene exactly as it was prescribed for you. Follow all directions on your prescription label. Your doctor may occasionally change your dose to make sure you get the best results. Do not use this medicine in larger or smaller amounts or for longer than recommended.
Take this medicine after eating a meal.
Taking a diuretic can make you urinate more often, which could disrupt your sleep if this happens at night. If you take triamterene only once per day, take it in the morning to reduce the chance of night-time urination.
While using this medicine, you may need frequent blood tests. Your kidney function may also need to be checked.
Your heart function may need to be checked using an electrocardiogram or ECG (also called an EKG).
This medicine can cause unusual results with certain medical tests. Tell any doctor who treats you that you are using triamterene.
If you need surgery, tell the surgeon ahead of time that you are using triamterene.
Store at room temperature away from moisture, heat, and light. Keep the bottle tightly closed when not in use.
Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.
This medicine may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.
Drinking alcohol with this medicine can cause side effects.
Do not use salt substitutes or low-sodium milk products that contain potassium. These products could cause your potassium levels to get too high while you are taking triamterene.
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