Talk:Clearance (pharmacology)

To be precise, isn't what this article refers to actually the clearance rate? While clearance itself actually refers to the process not the rate. honeydew 10:05, 8 December 2005 (UTC)

The term clearance has a general and a specific meaning. In general, clearance refers to the removal of substances from the body. But in renal physiology, clearance specifically refers to the volume of plasma per unit time that is cleared of a particular substance. You're right that it is a rate, but that's just assumed when you say renal clearance. It might be tempting to move this article to clearance rate (medicine) or something similar, except that few (if any) in medicine call it clearance rate -- it's just renal clearance. That's not to say this article shouldn't discuss the general term, though. --David Iberri (talk) 21:22, 4 March 2006 (UTC)

Definition, structure

I can't tell from the text what the definition is. Statements are unclear, and following the circular reasoning in the mathematical explanation, one would conclude that the definition follows from a formula derived from the definition:

Its definition follows from the differential equation that describes exponential decay and is used to model kidney function and hemodialysis machine function:

$V{\frac {dC}{dt}}=-K\cdot C+{\dot {m}}\qquad (1)$

• K is the clearance [mL/min] or [m³/s]
• C is the concentration [mmol/L] or [mol/m³] (in the USA often [mg/mL])

From the above definitions it follows that ${\frac {dC}{dt}}$ is the first derivative of concentration with respect to time, i.e. the change in concentration with time.

.....

Equation 1 is derived from

$\Delta m_{body}=(-{\dot {m}}_{out}+{\dot {m}}_{in}+{\dot {m}}_{gen.})\Delta t\qquad (2)$

Since

$m_{body}=C\cdot V\qquad (3)$

and

${\dot {m}}_{out}=K\cdot C\qquad (4)$

..... gives:

$V{\frac {dC}{dt}}=-K\cdot C+{\dot {m}}\qquad (1)$

Formula (4) effectively defines Clearance as mass removal rate divided by concentration. So how can a differential equation in which it's already used be the basis for it? Unless the point is that using that definition, the resulting function exponentially decays, in agreement with observations, thereby validating the assumption made.

As for the steady state: for deciding steady state conditions (at t infinity), using the general solution is overkill. By it's definition, all derivatives are zero in steady state, making the left part of equation (1) zero, giving after rearanging $C_{SteadyState}={\frac {\dot {m}}{K}}\qquad$ (see page 11 from the article's own reference )

The above equation (10b) makes clear the relationship between mass removal and clearance. It states that (with a constant mass generation) the concentration and clearance vary inversely with one another. If applied to creatinine (i.e. creatinine clearance), it follows from the equation that if the serum creatinine doubles the clearance halves and that if the serum creatinine quadruples the clearance is quartered.

Shouldn't that be "makes clear the relationship between concentration and clearance"? And given cause and effect, "if the clearance halves the serum creatinine doubles", sound more logical, even when the creatinine concentrations are used to determine clearance.

The article has too much basic maths, even explaining what a first derivative is, and telling us that e is the basis of the natural logaritm. People who never heard of e would be better served with a link to the exponential function ...

I have no medical qualifications, maybe this is how it's being taught at universities? This sentence is way too long btw:

However, the mass removal rate is the same[5], because it depends only on concentration of free substance, and is independent on plasma protein binding, even with the fact that plasma proteins increase in concentration in the distal renal glomerulus as plasma is filtered into Bowman's capsule, because the relative increases in concentrations of substance-protein and non-occupied protein are equal and therefore give no net binding or dissociation of substances from plasma proteins, thus giving a constant plasma concentration of free substance throughout the glomerulus, which also would have been the case without any plasma protein binding.

DS Belgium (talk) 04:05, 20 October 2011 (UTC)

References

Mass generation rate

The term "mass generation rate" is used in the article, but not defined. I had trouble locating a definition for this term anywhere on the internet. — Preceding unsigned comment added by 63.138.92.98 (talk) 18:50, 13 December 2013 (UTC)

Can someone address Zero-order and First-order clearance?

I'm no expert on pharmacokinetics, but I think the last sentence of the first paragraph is wrong.

"Clearance is constant in first-order kinetics because a constant fraction of the drug is eliminated per unit time, but it is variable in zero-order kinetics, because the amount of drug eliminated per unit time changes with the concentration of drug in the blood.[1][2]"

My understanding, and correct me if I'm wrong, is that Clearance is variable in first-order kinetics as the amount of drug cleared is determined by a fixed fraction of the plasma concentration of the drug, which invariably changes as the drug is metabolized and excreted. While the clearance is constant in zero-order kinetics because the amount of drug cleared from the plasma is independent of the plasma concentration, so the rate is constant and dependent on enzyme activity.

Not sure who is watching this page but any input,correction or clarification would be welcomed. Drtcalla (talk) 11:17, 17 January 2014 (UTC)

It seems that not many people are watching! The page is correct on this point: Clearance is constant for first-order kinetics, and this actually follows from your observation that "the amount of drug cleared is determined by a fixed fraction of the plasma concentration of the drug". Remember that clearance is a volume of fluid per unit time, and it is this "volume per unit time" that is fixed. So, for a first order process, the Clearance is constant, but the excretion/metabolism rate falls over time. For a zeroth order process, the Clearance rises over time (although this parameter wouldn't usually be measured for a zeroth order process), but the excretion/metabolism rate is constant.Klbrain (talk) 09:25, 3 November 2015 (UTC)

I've just reverted another attempted 'correction' on this point. Drtcalla; the text was right: clearance is constant for a first order process. This is also discussed/referenced at Clearance (medicine). Klbrain (talk) 17:35, 1 February 2016 (UTC)

Failure to parse

I tried to build <math> around the formulas but they failed to parse. I have no idea why it didnt work. Wilson868 (talk) 07:36, 30 August 2022 (UTC)