"what about my water pill, doctor?"

This morning we briefly talked about the mechanism of action of furosemide (lasix). This drug is a loop diuretics that inhibits the Na-K-2Cl channel in the thick ascending limb of the loop of Henle on the luminal side.

The efficacy of Furosemide is dose-dependent, but a plateau is reached in which even higher doses produce no further diuresis (when all the channels are saturated). The bioavailability of furosemide is only about 50%, so IV is twice as potent as oral. The drug is renally cleared.

IV therapy is preferred in patients with decompensated heart failure initially because drug absorption may be slowed by decreased intestinal perfusion and mucosal edema.

Furosemide is a sulfonamide drug so can cause hypersensitivity reactions, but patients with a history of allergy to sulfonamide antibiotics usually tolerate furosemide with little cross-reactivity.

Another side effect furosemide to be aware of is ototoxicity.

Here is a review article on diuretic therapy.