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Old 03-30-2013
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Drug Drug Clearance vs Elimination

I think I can finally understand the concepts of pharmacokinetics, once I get these two principles down. I think it will all start making sense!

I understand Clearance very well from a Renal perspective. Quite simply, its the volume of plasma that is completely cleared of a substance, per unit time.

So that same concept I assume applies to pharmacokinetics. But now, we have a situation, where Clearance will always be the same for drugs which obey 1st order kinetics.

The formula for CL = Rate of Elimination / Cp

Makes sense.

In 1st order kinetics, we said CL is constant. But Rate of Elimination is not constant. At first, the rate of elimination will be high, and as time goes on, it will get lower and lower. This is based from manipulating the equation:

Rate of Elimination = CL x Cp

CL is constant, so as Cp decreases, Rate of Elimination starts out high, and ends up low.

Now lets turn to ZERO order kinetics. We know that CL is NOT constant. But Rate of Elimination IS constant. (is this correct?)

Am I missing anything here?
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