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Triamterene and hydrochlorothiazide are diuretics that are prescribed together for people who require strong treatment for both high blood pressure, or hypertension; and edema, or swelling in the body that is caused by water retention. Although triamterene and hydrochlorothiazide can individually treat high blood pressure and edema on their own, using them together can provide a more effective treatment for each of these conditions when they exist at the same time. Triamterene and hydrochlorothiazide generally are dispensed in one combination pill.
Both medicines act on the kidneys but in different ways. Hydrochlorothiazide, which has been in use for many years to treat both high blood pressure and edema, causes sodium to be drawn out from the blood by acting on an area of the kidney known as the distal convoluted tubule. This helps lower blood pressure because excess sodium in the body can raise blood pressure. By eliminating sodium, less water is retained in the body, which also helps treat edema. Less water in the body also means less blood volume, which can decrease the resistance of blood flow in blood vessels, especially peripheral ones.
A drawback to taking hydrochlorothiazide is that it results in the kidneys also removing potassium from the blood while they try to reabsorb the sodium that is being removed from it. This can have adverse consequences. Losing too much potassium can often cause heart rhythm abnormalities.
This is why triamterene is often considered a better alternative to hydrochlorothiazide if potassium loss is a concern in certain therapeutic situations. Triamterene can lower blood pressure and reduce edema without removing potassium from the body. It accomplishes this by focusing its actions on a different part of the kidney, the collecting tubule, in a way that not only causes sodium to be drawn from the blood but also keeps the kidneys from trying to reabsorb it. This, in turn, keeps the kidneys from eliminating potassium at the same time.
Serious cases of edema that are also accompanied by hypertension might not lend themselves to effective treatment with either of these drugs if they are prescribed alone, however. A more potent therapy is achieved by combining triamterene and hydrochlorothiazide, often in a single pill. The patient then gets the benefit of a double-dose of the medications that treat edema, along with treatment for his or her hypertension in a manner that prevents the loss of potassium.