Diuretics are a broad group of medications that increase the urine filtration in the kidneys. The diuretics have different mechanisms of action, they usually increase loss of certain ions into the urine (especially sodium and potassium), which also causes excessive fluid loss.
Seemingly banal effect of these drugs has a huge impact in treatment of many diseases, especially those associated with accumulation of fluid in the body. A classic example is acute and chronic heart failure. Failing heart does not adequately pump the blood, which accumulates in the body. The result is shortness of breath and swelling. The diuretics increase fluid loss into the urine, thereby relieving the heart and causing disappearance of the symptoms. Similar effect has diuretic therapy in liver cirrhosis, when the portal hypertension causes formation of ascites. In addition, diuretics are used in combined therapy of high blood pressure.
The main side effect is potential dehydration, which may occur in too high dose of diuretic. Another possible result is a significant drop of blood pressure with weakness, dizziness and risk of fainting. Some stronger diuretics may damage kidney tissue and worsen the chronic renal failure. Another disadvantage is disruption of internal environment of the organism and ion imbalance. Especially dangerous are changes of serum level of potassium (hyperkalemia, hypokalemia).
Diuretics divide into several subgroups according to their specific effect.
These drugs are commonly used in heart failure. They have a very powerful effect, causing great loss of fluid, sodium and potassium. These diuretic can be administered in both oral and intravenous form. Main used substance is furosemide. In acute heart failure with massive swelling and shortness of breath (or even in lung edema), the loop diuretics are usually administered intravenously (intermittently or continuously) to ensure rapid and strong effect.
Main disadvantage is large loss of potassium, which may result in hypokalemia. Possible complications of this condition can be found in the relevant article.
These are less aggressive diuretics, which are used more for less severe forms of long-term heart failure and in treatment of hypertension. Again, they may cause excessive losses of ions and fluid, but not as dramatic as the loop diuretics. The basic substances of this group are hydrochlorothiazide and indapamide.
This group includes compounds such as spironolactone and compound amiloride. They have different mechanisms of action, but both increase the fluid loss by increased sodium excretion. Great thing is that these diuretics reduce the potassium loss into urine and increase the potassium concentration in blood. This may be either beneficial, or problematic. Potassium-sparing diuretics are great in combination with loop diuretics (see above) to prevent hypokalemia. On the other hand, they may cause dangerous hyperkalemia.
Diuretics are very important drugs in therapy of heart failure and hypertension. However, it is advisable to repeatedly monitor patient's blood minerals and blood pressure after the beginning of diuretic therapy to prevent the above-mentioned complications.