Re: Do diuretics shorten the half life of drugs that are extreted in urine?

From your explanation of your query, I think it can be safe to assume that you know pretty well how the kidney functions in terms of salt and water balance.

Even then, I'll begin with a short preview.
The basic functioning and anatomical unit of the kidney is the nephron - consisting of a glomerulus, a proximal collecting tubule (PCT), the loop of Henle and the distal collecting tubule(DCT) which ends in a collecting duct. Blood is ultrafiltered through the glomerular apparatus - what comes in the PCT is water and minerals like sodium (Na), Potsssium(K), urea, etc. The urine that we finally pass goes through various modificaions, such as reabsorption, secretion, concentration, dilution - all through its passage from the PCT, Loop of Henle, DCT to the collecting ducts and finally to the ureter, bladder, urethra and out of the body. Details on its functioning can be found in any textbook of human physiology.

What we are concerned with is the action of diuretics. Now, the word "diuretic" itself means "to pass more urine" (dont ask me if it is greek, latin or roman!!! [It's originally from the Greek, "diouretikós" -- Mod]). So, what diuretics basically do is to increase the amount of urine passed by the body. And they do so in various actions on different sites of the nephron - as the image below shows.

From the picture, it can be seen that among all the different actions, the common base is how the drugs manipulate the levels of Na and K in the urine, thereby causing more urine to pass.

Now, when it comes to drugs being excreted by the kidney, these drugs are filtered through the glomerulus and excreted out in urine without much interference from the Na-K dynamics of the nephron. But that does not mean that diuretics have no effect on such drugs or vice versa.

The interactions of diuretics with other drugs is mainly due to the Na-K dynamics which are altered, not only in the nephron, but also in the body. So, hypokalemia (decreased potassium in the body) due to diuretics causes enhanced toxicity of drugs like digitalis. Or for example, aminoglycoside anibiotics(streptomycin, amikacin) should not be used with diuretics because they potentiate their toxic effects on the kidney.

What it basically means is that diuretics have no effect on drugs being excreted by the kidney, unless that excretion is dependant on Na-K dynamics in the kidney (which is very very rare). Or in other words, the half life of the drug is not affected. The half life of the drug reflects the dosage to be given so that a therapuetic concentration is acheived in the body. And the half life changes only if there is some problem with the kidneys in ulrafiltration - say renal failure, where half life changes and so drug dosages change. Even doses of diuretics change.

Otherwise, there are plenty of drug interactions with diuretics and care should be taken while adding on a drug while somebody is taking diuretics