Liver vs kidney excretion?

[ibarne242]

I've been confused, because lately a lot of drugs are, supposedly (according to my pharm book and wikipedia), have liver and kidney excretions that don't add to 100%. Chloramphenicol, for ex, is "excreted by kidney (5-15%) and liver (5%)." Like...what the hell does this mean? I'm pretty sure once a drug gets into the body, it's all going to have to eventually be excreted.
Also, is the "fecal" route the same as biliary (liver) excretion?
My guess is maybe when these percentages don't add to 100, they mean the rest is just not absorbed at all, but that makes little sense to me as many of these are IV options too and also you take bioavailability into account.
Can anyone offer some insight?

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[Drrrrrr. Celty]

Don't over think it. The kidney v.s liver metabolism %s are important not for you knowing that something is peripherally converted or etc, but rather to know whether you should use a drug in a patient with poor liver function, with high amount of cyp-450 modifying agents, with liver enzyme elevating properties, or in patients with chronic kidney disease.

So for example, a drug that is metabolized exclusively by the kidney isn't indicated by a patient with end stage chronic kidney disease. You'd use a med that has more liver metabolism. Or in a patient with poorer function of kidney how much they'd probably be able to modify the dose to get to the therapeutic steady state and keep them out of the non-therapeutic/toxic range.


But in short, things are also peripherally converted and broken down too. Drugs accumulate outside of the circulatory system and exit by sweat, breathing out, and by shedding too.