Hydrochlorothiazide is a prescription medication belonging to a class of drugs called thiazide diuretics. Often called “water pills,” these medications prompt the kidneys to remove unneeded water and salt from the body through urine. It is available as tablets, capsules, and a liquid solution. This drug may be used by itself or as part of a combination therapy.
Medical Uses of Hydrochlorothiazide
Hydrochlorothiazide is primarily prescribed to manage high blood pressure (hypertension) and fluid retention (edema). Untreated high blood pressure can strain the heart and arteries, potentially leading to damage of the brain, heart, and kidneys. By reducing the total volume of fluid in the blood vessels, the medication lowers blood pressure and reduces how hard the heart has to work.
The medication is also effective in treating edema. This fluid retention can be a symptom of medical problems like heart failure, liver disease, and certain kidney diseases. It can also be caused by some medications, such as corticosteroids or estrogens. Hydrochlorothiazide helps alleviate the swelling by increasing urine output, which removes the accumulated fluid.
Beyond its main applications, hydrochlorothiazide has some off-label uses. It can be prescribed to prevent a specific type of kidney stone made from calcium oxalate by reducing the amount of calcium the kidneys excrete into the urine. It may also be used to manage a condition called diabetes insipidus.
Mechanism of Action
The primary action of hydrochlorothiazide occurs in the kidneys, targeting the distal convoluted tubules. These tubules are responsible for reabsorbing a portion of the sodium filtered from the blood. The drug inhibits the sodium-chloride symporter, a transport system in the walls of these tubules.
By blocking this transporter, hydrochlorothiazide prevents the reabsorption of sodium and chloride ions back into the bloodstream. Because water follows sodium to maintain balance, more water is kept within the tubules. This action leads to an increased excretion of both salt and water from the body as urine, a process called diuresis.
This diuretic effect reduces the overall fluid volume in the body, including the plasma volume in the blood. Over a longer period, hydrochlorothiazide is also thought to help relax the smooth muscles in blood vessel walls, which can further contribute to a sustained reduction in blood pressure.
Potential Side Effects and Risks
Common Side Effects
Common side effects, particularly when first starting the medication, include increased urination, dizziness, headache, and weakness. Some people may also experience tingling in their hands and feet, muscle spasms, or diarrhea. Dizziness can be more pronounced when standing up quickly, so moving slowly can help reduce this effect.
Serious Side Effects
Some side effects require prompt medical attention. Severe dehydration may present with a very dry mouth, increased thirst, confusion, or dark yellow urine. Significant electrolyte imbalances, like low potassium or sodium, might cause muscle pain, weakness, or an irregular heartbeat. The drug can also trigger a gout attack or cause kidney problems, indicated by decreased urine output and swelling.
Important Risks and Interactions
Certain individuals should not take hydrochlorothiazide, including those with an allergy to it or other sulfonamide-based “sulfa” drugs. People who are unable to urinate (anuria) should also avoid this medication. Caution is advised for patients with liver disease, kidney disease, diabetes, or a history of gout, as the medication can worsen these conditions.
This drug can interact with other medications, altering their effects. It can increase the effects of other blood pressure-lowering drugs, potentially causing blood pressure to drop too low. It may also interact with:
- Digoxin, a heart medication, which can be problematic if potassium levels become low
- Lithium
- Certain diabetes medications
- Corticosteroids like prednisone
Provide a full list of all medications, including non-prescription drugs and supplements, to a healthcare provider.
Dosage and Administration Guidelines
A healthcare provider determines the dosage of hydrochlorothiazide based on the condition and individual response. For high blood pressure in adults, a typical starting dose is 12.5 mg or 25 mg once a day, not to exceed 50 mg daily. For edema, the adult dosage can range from 25 mg to 100 mg daily, taken as a single dose or divided into two. A doctor might recommend an intermittent schedule, such as every other day, to reduce the risk of electrolyte imbalance.
Hydrochlorothiazide is usually taken once daily in the morning to prevent frequent urination during the night. If a dose is missed, take it as soon as remembered, but skip it if it is almost time for the next dose to avoid doubling up. Taking too much can lead to an overdose with symptoms like severe dehydration and dizziness. In case of a suspected overdose, seek immediate medical attention or contact a poison control center.