Calcium

A review of the research literature indicates that triamterene may increase calcium loss.¹ The importance of this information is unclear.

Folic acid

Triamterene is a weak folic acid antagonist that has been associated with folic acid-deficiency anaemia in people already at risk for folic acid deficiency.² However, people treated long term with triamterene, without additional risk for folic acid deficiency, were found to have normal folic acid levels and no signs of folic acid deficiency.³ The use of multivitamin supplements containing folic acid appears to diminish the occurrence of birth defects associated with triamterene. According to one study,⁴pregnant women who took folic acid–containing multivitamin supplements in addition to their prescription drugs had fewer babies with heart defects and deformities of the upper lip and mouth.

One study showed that people taking diuretics for more than six months had dramatically lower blood levels of folic acid and higher levels of homocysteine compared with individuals not taking diuretics.⁵ Homocysteine, a toxic amino acid by-product, has been associated with atherosclerosis. Until further information is available, people taking diuretics for longer than six months should probably supplement with folic acid.

Magnesium

Preliminary research in animals suggests that triamterene may inhibit the urinary excretion of magnesium.⁶ It is unknown if this same effect would occur in humans. Persons taking more than 300 mg of magnesium per day and triamterene should consult with a doctor as this combination may lead to potentially dangerous increases in the level of magnesium in the body. The combination of triamterene and hydrochlorothiazide would likely eliminate this problem, as hydrochlorothiazide may deplete magnesium.

Potassium

As a potassium-sparing drug, triamterene reduces urinary loss of potassium, which can lead to elevated potassium levels.⁷ People taking triamterene should avoid potassium supplements, potassium-containing salt substitutes (Morton Salt Substitute, No Salt, Lite Salt, and others) and even high-potassium foods (primarily fruit). Doctors should monitor potassium blood levels in patients taking triamterene to prevent problems associated with elevated potassium levels.

However, some medications (for example, Dyazide, Maxzide) contain the combination of the potassium-sparing drug triamterene and the potassium-depleting drug hydrochlorothiazide. With the use of these combination medications, potassium excess and potassium depletion are both possible. People taking these drugs should have their potassium levels monitored by a doctor to determine whether their potassium intake should be increased, reduced, or kept the same.

Sodium

Diuretics, including triamterene, cause increased loss of sodium in the urine. By removing sodium from the body, diuretics also cause water to leave the body. This reduction of body water is the purpose of taking diuretics. Therefore, there is usually no reason to replace lost sodium, although strict limitation of salt intake in combination with the actions of diuretics can sometimes cause excessive sodium depletion. On the other hand, people who restrict sodium intake and in the process reduce blood pressure may need to have their dose of diuretics lowered. People taking triamterene should talk with their prescribing doctor before severely restricting salt.