Loop diuretics are highly efficacious drugs that mainly act in the ascending limb of the loop of Henle. Furosemide and bumetanide are the main representants of this group. They almost completely block reabsorption of Na+ and Cl- ions in the ascending loop by blocking the Na+/K+/2Cl-co-transporter. Neither Na+ ions nor K+ ions are reabsorbed. As a result, the NaCl concentration drops, which leads to decreased reabsorption of water and thus more diuresis. By changing the exchange of ions, the loop diuretics also cause a potential difference between the apical and basal membrane. Positive ions such as Mg2+ and Ca2+ cannot flow down the gradient into the interstitium anymore and will be excreted. Furthermore, loop diuretics increase renal blood flow and venodilatation.
Indications for loop diuretics are the treatment of acute pulmonary edema in patients with heart failure and hypertension in patients with renal failure. Edema in patients with nephrotic syndrome and hypercalcemia are other special indications.
Hypokalemia, hypomagnesiemia, hyperuricemia (gout), contraction alkalosis and decline in renal function as result of underfilling (especially in elderly), hepatic encephalopathy (liver cirrhosis) and ototoxicity are the main adverse effects. Dizziness, hypotension, and cramps are symptoms that may accompany these effects. It is important that the electrolyte balance and renal function is monitored closely during treatment with loop diuretics. Moreover, a combination with potassium-rich diet is recommended.
I. The kidneys are responsible for the clearance of loop diuretics
II. Hyponatremia, as an adverse effect of loop diuretics, poses danger to the cardiac function.
Extra info: Loop diuretics are cleared by the kidneys. Hypokalemia, not hyponatremia, can cause arrhythmias.