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metolazone, Zaroxolyn, Diulo, Mykrox

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GENERIC NAME: metolazone

BRAND NAME: Zaroxolyn; Diulo; Mykrox

DRUG CLASS AND MECHANISM: Metolazone is a diuretic ("water pill") used in the treatment of high blood pressure and fluid accumulation. It works by blocking salt and fluid retention in the kidneys, thereby increasing urinary output of salt and water (diuresis). Although it is not a true thiazide, metolazone is chemically related to the thiazide class of diuretics, and works in a similar manner. Zaroxolyn is the original formulation of metolazone, and Diulo is similar. The absorption of these two drugs is relatively incomplete. Mykrox has more complete absorption. Therefore, less Mykrox needs to be given to have the same effects as a larger dose of Zaroxolyn or Diulo. Metolazone was approved by the FDA in 1973.

GENERIC AVAILABLE: no

PRESCRIPTION: yes

PREPARATIONS: Zaroxolyn or Diulo: Tablets: 2.5mg, 5mg, 10mg. Mykrox: Tablets: 0.5mg.

STORAGE: Tablets should be stored at room temperature, 15-30°C (59-86°F).

PRESCRIBED FOR: Metolazone is used in the treatment of high blood pressure, in the management of congestive heart failure, and for the treatment of edema.

DOSING: The dosing of metolazone is individualized. It is important to realize that Mykrox should not be substituted for Zaroxolyn or Diulo (or vice versa), since the two drugs differ greatly in their potency. Zaroxolyn and Diulo, however, are equivalent in potency and are interchangeable.

DRUG INTERACTIONS: Metolazone can lower blood potassium and magnesium levels. This is especially true in patients who are also taking "loop" diuretics such as furosemide (Lasix), bumetanide (Bumex), torsemide (Demadex ) Low potassium and magnesium levels can lead to heart rhythm abnormalities, especially in patients already taking digoxin (Lanoxin).

Blood uric acid levels can increase during metolazone treatment, but precipitation of gout due to the increase is rare. Metolazone reduces excretion by the kidneys of lithium and can lead to lithium toxicity in patients being treated with lithium.

Nonsteroidal anti-inflammatory agents (NSAIDs) such as ibuprofen (Motrin), naproxen (Naprosyn), and nabumetone (Relafen) can reduce the effectiveness of metolazone by interfering with the excretion of salt and water.

PREGNANCY: Metolazone should not be used during pregnancy unless absolutely necessary.

NURSING MOTHERS: The American Academy of Pediatrics recommends that breast-feeding be avoided during the first month in patients receiving thiazide diuretics because thiazide diuretics may cause there to be less production of milk..

SIDE EFFECTS: Metolazone generally is well tolerated. Hypokalemia (low blood potassium), hyponatremia (low blood sodium), and hypomagnesemia (low blood magnesium) occur commonly during metolazone therapy. Hypercalcemia (high blood calcium) also may occur. Thiazide diuretics are known to increase the amount of uric acid in the blood, but gout (which is associated with high uric acid) is rarely reported. Metolazone can cause high blood sugar in diabetic patients. About 1 out of every 10 patients report dizziness, lightheadedness, and headache. Fatigue has been reported in 1 out of every 25 patients. About 1 out of every 50 patients reports nausea, vomiting, abdominal pain, or constipation.

Reference: FDA Prescribing Information

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