Most physicians do not understand pharmacology and pharmacokinetics. We use Lasix (furosemide) because we have always used furosemide. As an academic hospitalist, we often have patients admitted with heart failure (either right sided or left sided) who have gained significant fluid weight despite taking significant oral doses of furosemide. When they get admitted we start with IV furosemide and amazingly they pee like racehorses.

How many of us remember that oral furosemide is variably absorbed, with a general range of 20%-80%? You may not remember that, or you might just be in the habit of using Lasix. Lasix has a great name. It was generic when I was a medical student (71-75). It is a magic drug. But should it be our first line oral loop diuretic.

We have two other good generic choices – bumetanide (Bumex) and toresamide (Demadex). Both drugs have consistent absorption in the range of 95%. Some data suggest that torsemide use improves outcomes, perhaps even all-cause mortality. Torsemide has some anti-aldosterone properties in addition to blocking the NaK-2Cl channel.

Recently we had another patient taking 80 mg of Lasix twice daily – and he had gained 50 pounds. IV furosemide worked beautifully. We tried Bumex 2mg (the rough conversion between furosemide and bumetanide is 40 to 1) and he continued diuresing.

So why do we start with furosemide? And I am guilty also. Can anyone explain it or disagree?