Pharmacology: Clearance vs Volume of Distribution

AI Thread Summary
The discussion centers around the relationship between Volume of Distribution (Vd), elimination constant (k), and Clearance (Cl) in pharmacokinetics. It highlights that Vd is calculated as the product of k and Cl, raising questions about the proportionality of clearance to volume of distribution. One participant expresses confusion about how clearance, defined as the mass of drug eliminated over time divided by plasma concentration, relates to varying volumes of distribution. They note that a larger volume suggests more mass absorption, leading to a proportionality with eliminated mass. Another participant clarifies that the elimination constant should be positioned differently in the equation, and they discuss the dependency of elimination rate on plasma concentration, questioning how this remains consistent across individuals with different Vd. Overall, the conversation delves into the complexities of pharmacokinetic relationships and the implications of varying physiological parameters.
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Hi,

I understand that Volume of Distribution (Vd) = elimination constant (k) * Clearance (Cl), but I can't visualize why clearance would be proportional to volume of distribution. Can someone help explain this to me? I feel like it should be a more complicated relationship. Clearance = Mass Drug eliminated/time/Concentration in Plasma. How are these variables changing with different volumes of distribution?
Thanks.
 
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Distribution in a larger volume -> more mass gets absorbed, and clearance is proportional to the eliminated mass.
I think the elimination constant should be at the other side, or taken as inverse value, otherwise its definition disagrees with the wikipedia article.
 
Hi thanks you're right the elimination constant should be on the other side. With regards to the eliminated mass, I'm still a bit confused because the rate of elimination of the mass is dependent on the concentration of the drug in the plasma which should be the same between individuals even if they have different volumes of distribution?
 
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