What to Know About Microzide (Hydrochlorothiazide)

Hydrochlorothiazide is a prescription diuretic, more commonly known as a "water pill," used to help the body eliminate excess water. Hydrochlorothiazide reduces the volume of blood in the body by stimulating kidney function. The kidneys play a large role in sodium reabsorption, meaning hydrochlorothiazide increases the frequency which kidneys produce urine. This excess fluid is eliminated from the body through the urine. This excess water may be building up due to high blood pressure, heart failure, chronic kidney disease, liver disease, or inflammatory conditions of the body.

The most common brand name version of hydrochlorothiazide is Microzide. However, other brand names forms of hydrochlorothiazide include Zide, Aquazide, Thiazide, and Hydrocot.

Hydrochlorothiazide is a Food and Drug Administration (FDA) approved drug for the use in treating edema or fluid buildup associated with congestive heart failure, cirrhosis of the liver, and therapies such as synthetic corticosteroids and estrogen.

Other FDA-approved uses for hydrochlorothiazide include treating kidney diseases such as chronic kidney failure, nephrotic syndrome, and high blood pressure. Despite its effectiveness in treating some kidney conditions, hydrochlorothiazide does not affect blood pressure.

Off-Label Uses

Hydrochlorothiazide has been approved to treat some but not all kidney conditions.

One of the most popular off-label uses for hydrochlorothiazide is to prevent recurrent calcium nephrolithiasis, more commonly known as kidney stones. When taken on a regular basis, hydrochlorothiazide effectively regulates the urine levels of calcium in patients who frequently develop kidney stones.

Another off label-use for hydrochlorothiazide is for the treatment of lithium-induced diabetes insipidus. Diabetes insipidus is a form of diabetes which develops from an imbalance of bodily fluids. These bodily fluids begin to accumulate in response to inadequate production of antidiuretic hormones in the brain. A hormone change such as this can be triggered by heightened blood levels of the medication lithium.

Though effective in treating conditions such as bipolar disorder, lithium has harmful side effects when levels are even slightly higher than normal. While hydrochlorothiazide assists in regulating fluid levels which result from lithium-induced diabetes insipidus, this medication does not address the root cause of the disease.

Lithium-induced diabetes insipidus should be properly addressed by balancing and maintaining levels of lithium in the bloodstream.

A patient should undergo a thorough medical history and evaluation before being prescribed hydrochlorothiazide. This will ensure the patient does not have any underlying medical conditions or interacting prescription medications which will cause unsafe or harmful side effects.

Precautions and Contraindications

Hydrochlorothiazide should not be taken by women who are pregnant and have an edema-related condition causing fluid buildup. Taking hydrochlorothiazide for this purpose may cause a redistribution of vital fluids in the body, placing a fetus at risk for injury. However, hydrochlorothiazide can be taken by pregnant women experiencing fluid buildup as a result of their pregnancy.

This medication should not be taken by pregnant women at risk for developing toxemia, as this drug is not approved for the prevention of toxemia. It also should not be taken by individuals with sensitivities to the drug or other sulfonamide-based drugs.

Hydrochlorothiazide should not be taken by individuals with anuria, also known as the inability of the kidneys to produce urine.

All patients taking hydrochlorothiazide should be closely monitored to prevent electrolyte imbalance, especially if the patient frequently vomits as a result of the medication. This may come in the form of hyponatremia, hypochloremic alkalosis, and hypokalemia.

Signs of electrolyte imbalance may include:

• Dry mouth and excessive thirst
• Increased fatigue
• Muscle weakness
• Confusion
• Low blood pressure
• Low heart rate
• Muscle cramps
• Low urine output
• Nausea and vomiting

When under observation for electrolyte imbalance, patients should also be monitored for severe complications such as cardiac arrhythmia.

If urine output is increased as a result of hydrochlorothiazide, it may also increase the urinary output of magnesium. This can cause the body to enter a state of hypomagnesemia.

Hyperglycemia may occur in patients who take hydrochlorothiazide. For this reason, patients with diabetes may require adjustments to their doses of insulin.

Other Diuretics

• Loop-acting diuretic: This type of drug lowers the amount of water in the body and increases urine output. Examples of these drugs are Bumex, Demadex, Edecrin, and Lasix.
• Potassium-sparing diuretic: This type of drug helps the body retain potassium while shedding the fluid buildup. Examples of these drugs are Aldactone, Dyrenium, and Midamor.
• Thiazide diuretic: This type of drug lowers the amount of sodium and water in the body. Examples of these drugs are Aquatensen, Hydrochlorothiazide, Diucardin, Trichlorex, Metolazone, Indapamide, and Diuril.

Hydrochlorothiazide is available in 12.5 milligrams (mg), 25 mg, and 50 mg tablets. It is typically recommended adults with edema take 25 mg to 100 mg of hydrochlorothiazide daily.

Adults with high blood pressure should take 25 mg of hydrochlorothiazide daily. Doses for high blood pressure may be increased to 50 mg daily if the patient tolerates the starting dose.

Patients who take more than 50 mg daily of hydrochlorothiazide are at risk for significantly lowered potassium levels.

All listed dosages are according to the drug manufacturer. Check your prescription and talk to your doctor to make sure you are taking the right dose for you.

When given to older patients, doses of hydrochlorothiazide are typically 12.5 mg once daily. When prescribed for infants, hydrochlorothiazide is typically taken according to weight. A dose of 0.5 mg to 1 mg per pound per day is the standard formula.

For infants less than 6 months old, doses are typically 1.5 mg per pound per day. Doses often must be split into two for these infants less than 6 months old to ensure the drug is adequately tolerated.

How to Take and Store

Hydrochlorothiazide is slightly less effective when taken with food. This drug should be taken as per your doctor’s instruction in accordance with your tolerance to its effects.

Hydrochlorothiazide should be stored in a room between 20 to 25 degrees Celsius (68 to 77 degrees Fahrenheit).

As with all medications, hydrochlorothiazide may cause side effects.

Common

Common side effects which may result from taking hydrochlorothiazide include:

• Muscle spasms
• Muscle weakness
• Diarrhea
• Vomiting
• Constipation
• Gastrointestinal discomfort
• Impotence
• Rash
• Fever
• Minor electrolyte imbalance
• Dizziness
• Headache
• Restlessness

Severe

Severe side effects which may result from taking hydrochlorothiazide include:

• Orthostatic hypotension (especially when combined with sedative drugs or alcohol)
• Pancreatitis
• Jaundice
• Anorexia
• Aplastic anemia
• Leukopenia (low white blood cells) or agranulocytosis (severe low white blood cell count)
• Thrombocytopenia (low platelet count)
• Anaphylactic reactions
• Respiratory distress
• Renal failure or renal dysfunction
• Blurred vision

Hydrochlorothiazide interacts with the following prescription drugs:

• Barbiturates
• Narcotics
• Antidiabetic drugs
• Antihypertensive drugs
• Colestipol resins for gastrointestinal disorders
• Corticosteroids for inflammation
• Muscle relaxers
• Lithium for mood disorders
• Non-steroidal anti-inflammatory drugs (NSAIDs) for over-the-counter pain relief

Hydrochlorothiazide can also interact with laboratory tests for parathyroid function, meaning the drug should be discontinued before drawing the blood for this test.

A black box warning is attached to hydrochlorothiazide due to its ability to cause fetal mortality in women using the drug to treat high blood pressure.