Being a clinical pharmacist, you get asked a lot of questions about the differences amongst agents in the same class. The issue of differences between furosemide versus torsemide recently came up. I figured I would use the blog to cover some of those differences.

Furosemide Versus Torsemide: Half-life

When comparing two agents in the same class, one of the first characteristics to consider is half-life. In the situation of comparing furosemide versus torsemide, the half-life is somewhat longer for torsemide. For torsemide, the half-life is about 3.5 hours, while with furosemide (under normal kidney function) it is about 1-2 hours.

References from package insert: furosemide; torsemide

I don’t think that there is a strong clinical impact because of this modest difference. You may have effects that last a little bit longer with the torsemide. This could be good or bad. If your patient is complaining about urinary frequency that lingers into the night, there is potential that torsemide with a longer half-life may have more potential to cause this even if taken earlier in the day. If you want the diuretic effect to last longer, or happen to be using a loop diuretic for hypertension, this longer half-life may give you a little bit longer effect.

Furosemide Versus Torsemide: Bioavailability

Another important consideration that can impact dosing is bioavailability. This is particularly important when converting from IV to oral. Furosemide has an oral bioavailability of around 60%. Torsemide is closer to 80%. This does allow for a little easier conversion as torsemide is closer to a 1:1 ratio of oral to IV.

Furosemide Versus Torsemide: Metabolism Versus Excretion

Furosemide is eliminated from the body, primarily through excretion in the urine. Torsemide undergoes significant hepatic metabolism through CYP2C9. This could be a significant clinical interaction to think about. With furosemide, since it is renally eliminated, it is also important to remember that renal impairment could increase the half-life. Listen to the basics on loop diuretics on this podcast.

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