Active Ingredients

Hydrochlorothiazide – Effect, Application & Risks


Hydrochlorothiazide is a diuretic drug and is considered the prototype of the thiazide diuretics . The active ingredient is used, among other things, to treat edema.

What is hydrochlorothiazide?

Hydrochlorothiazide is a diuretic. Diuretics are drugs with a fairly high therapeutic index. They are mainly used to flush water out of the human body. There are different types of diuretic drugs. Along with the potassium-sparing diuretics and aldosterone antagonists, thiazide diuretics are among the best-known diuretics.

Thiazide diuretics such as hydrochlorothiazide have a wide range of uses. They are used, among other things, to treat high blood pressure or heart failure . The thiazide diuretics are usually well tolerated, but can also result in electrolyte imbalances due to their flushing effect .

Hydrochlorothiazide has been banned from use by athletes by the World Anti-Doping Agency. Although the drug does not increase performance directly, it is one of the so-called masking agents. These can complicate the detection of doping substances. Hydrochlorothiazide dilutes the urine so much that a doping test in the urine is hardly possible.

Pharmacological action

Hydrochlorothiazide acts on the distal tubules of the nephron . The nephron is the smallest functional unit of the kidney . It consists of a kidney corpuscle and a tube system connected to it, the so-called tubular system. Primary urine is filtered in the nephron. Water and various other substances are recovered in the tubular system before the so-called secondary urine is excreted via the urinary tract .

Hydrochlorothiazide inhibits the sodium chloride cotransporter on the luminal membrane of cells in the tubular system. In higher doses, the drug also inhibits carbonic anhydrase. As a result, the kidneys excrete more sodium chloride and thus also water. In addition, fewer calcium ions and more magnesium ions are excreted. Due to the increased calcium retention, hydrochlorothiazide can also lead to increasing bone density in patients with osteoporosis .

The bioavailability of hydrochlorothiazide is 70 percent. The duration of action is 6 to 12 hours. The active ingredient is then excreted almost unchanged via the kidneys.

Medical Application & Use

Hydrochlorothiazide is primarily used to treat essential arterial hypertension . Rarely, however, is the active ingredient administered on its own. The therapy is usually carried out in combination with beta blockers or ACE inhibitors .

Hydrochlorothiazide is also used in heart failure. Here, the drug is usually used in combination with loop diuretics. These serve to mobilize edema, while hydrochlorothiazide serves to excrete water. Since hydrochlorothiazide increases the retention of calcium ions, it is also used in the treatment of osteoporosis. The recovered calcium can increase the patient’s bone density.

Another indication for the use of hydrochlorothiazide is hypercalciuria. This is an increased excretion of calcium in the urine. Bone metastases, vitamin D intoxication, sarcoidosis or Bartter syndrome are possible causes of such hypercalciuria. Since the increased excretion of calcium can lead to urinary stones , hydrochlorothiazide is used prophylactically in these cases.

Risks & side effects

Basically, hydrochlorothiazide is well tolerated, but various side effects can develop due to the loss of electrolytes. There is often a reduced level of potassium and sodium in the blood . Magnesium and chloride are also reduced. On the other hand, the calcium level in the blood is increased. Dry mouth and thirst are typical side effects.

At higher doses, weakness , dizziness , muscle pain , and muscle cramps may also occur. Patients suffer from heart palpitations and reduced blood pressure. In particular, when changing from lying to standing , they show orthostatic regulation disorders with dizziness.

At high doses, urination can be very excessive. As a result of dehydration and hypovolemia , i.e. the reduced amount of circulating blood, the blood thickens. This increases the risk of developing thrombosis or embolism , particularly in older patients or in patients with venous diseases . Fatigue , abnormal sleepiness, paralysis , or paralysis may occur as a result of hypokalemia . Constipation and bloating are also common side effects of hydrochlorothiazide.

During treatment, elevated levels of uric acid in the blood can occur, ultimately leading to gout attacks . Furthermore, an increase in blood lipids ( triglycerides and cholesterol ) is often observed. Occasionally the urinary substances creatinine and urea also increase in the blood.

A feared side effect of therapy with hydrochlorothiazide is pancreatitis . Inflammation of the pancreas can be life-threatening. Rarely, allergic skin reactions such as itching , exanthema or wheals occur when hydrochlorothiazide is taken . Acute kidney inflammation , vascular inflammation and anemia are also rare side effects. Some patients may also develop erectile dysfunction or vision problems while taking hydrochlorothiazide .

Thiazide diuretics such as hydrochlorothiazide should not be used in severe renal or hepatic dysfunction. Severe electrolyte imbalances such as hypokalemia , hyponatremia , and hypercalcemia are also contraindications. The use of hydrochlorothiazide is dangerous in the case of digitalis intoxication and cardiac arrhythmias . Likewise, hydrochlorothiazide must not be used in the case of an allergy to sulfonamides. Ideally, the doctor should also prescribe a different diuretic during pregnancy and breastfeeding .

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.