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Loop Diuretics

Drugs in medicine

Drugs in medicine

Introduction

Loop diuretics are the strongest type of diuretic – they cause an increase in the excretion of sodium and water from the kidney. They are very effective, and prevent the reabsoprtion of about 25% of filtered sodium.
Loop diuretics find their way into the tubule in the proximal region, via anion exchange (probably mainly for sodium). They bind to the sodium / potassium / chloride channel, in the thick ascending loop of Henle and inhibit chloride reabsoprtion. Thus this prevents this channel from functioning properly, and sodium is not reabsorbed. This prevents the formation of a very concentrated fluid in this region – as less sodium is reabsorbed, so less water is reabsorbed via osmosis.
Loop diuretics have a short half-life, and when they are stopped, there is rebound sodium retention, and thus short-term they aren’t much use.
They remain effective even in advanced renal failure, however you may need a pretty large dose!
When given intravenously, these drugs have a venodilating effect that cause pooling of blood and can be particularly useful in left ventricular failure.
They also cause vasodilation, but because of their short duration of action they are rarely used to treat hypertension.
They are absorbed from the gut but there is wide individual variation (10-90% depending on the individual). With normal kidney function, their half-life is short. They are excreted by the kidney.
The kidney is complicated, if you haven’t already, you might want to read about renal physiology to help understand how diuretics work.

Examples

Loop diuretics e.g. furosemide (aka frusemide), bumetanide

Unwanted effects

Indications and Uses

Dose

References

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