Comments for Learn PK/PD

Comment on Why Cmax is a continuous variable and tmax is a categorical variable by Nathan Teuscher

Nathan Teuscher — Fri, 24 May 2013 01:35:58 +0000

Helmut, thank you for the comment. Variables that have a finite number of possible values are called discrete, nominal, or categorical. All three terms can be used to differentiate a variable that has finite possible values from a variable with infinite possible values (a continuous variable). In many statistics textbooks, these terms (discrete, nominal, categorical) are used as synonyms.

Comment on Why Cmax is a continuous variable and tmax is a categorical variable by Helmut

Helmut — Fri, 24 May 2013 01:11:13 +0000

Almost. tmax is a discrete variable. Categorial ones are e.g. gender, race, etc.

Comment on Understanding volume of distribution by Nathan Teuscher

Nathan Teuscher — Mon, 20 May 2013 18:12:25 +0000

Basil, Thank you for your questions. Here are brief responses:
1. Total blood volume includes plasma as well as the cellular components of blood. It has been estimated that total blood volume is about 15 L.
2. It is possible that Vd is less than plasma volume. Remember, that volume of distribution is simply a proportionality factor between measured concentrations and amount of drug in the body. While this situation is rare, it is possible.
3. As I mentioned in answer #2, Vd is a proportionality factor. If you don’t know the absolute bioavailability of a drug, then you cannot calculate Vd, you can only calculate Vd/F. However, if you know the absolute bioavailability, then you are calculating the actual proportionality factor between the amount of drug and concentration of drug in the body. This number is unaffected by the bioavailability, therefore it would be incorrect to say that Vd is large because of low bioavailability. If on the other hand, you don’t know the absolute bioavailability of your compound, then large values of Vd/F could be due to low bioavailability or wide tissue distribution.

I hope that helps.

-Nathan

Comment on Understanding volume of distribution by Nathan Teuscher

Nathan Teuscher — Mon, 13 May 2013 15:06:22 +0000

In most cases, the volume of distribution does not change with dose. However it is possible that distribution is dose-dependent.

Comment on Understanding volume of distribution by Basil

Basil — Mon, 13 May 2013 12:55:12 +0000

Dear Nathan,

I have a few questions:

1) I might be missing something but the actual volume of blood in the body should be about 5.5 liter (male). How come that in your table it is 15?

2) Is it possible that Vd

3) Imagine that you work w poorly absorbed drug w absolute BA of c.a. 1%. So you administer it orally and measure a tiny fraction of it in the plasma. Will your PK model show a big Vd value because it thinks that all the drug sits in the tissues but instead 99% is excreted w feces?

Thank you in advance!

Comment on Understanding volume of distribution by roohi

roohi — Mon, 13 May 2013 09:15:29 +0000

so does changing the dose change the volume of distribution ,for the same individual ?

Comment on Review of Phoenix Connect Software Tool by Simon

Simon — Tue, 07 May 2013 13:33:40 +0000

I hope others find this review useful – I will be presenting a free half-day presentation and workshop on Connect the Tuesday afternoon before PAGE this year in Glasgow, UK http://www.pharsight.com/training/course_display_new.php?details_id=98

Simon

Comment on Accumulation: What it means and how to calculate it by Luis, Dominican Republic

Luis, Dominican Republic — Sun, 05 May 2013 17:29:09 +0000

Very good. Maybe has to be more comprehensible with more examples better applicable to the trials studies.

Comment on Understanding volume of distribution by Nathan Teuscher

Nathan Teuscher — Fri, 26 Apr 2013 14:30:21 +0000

Nabeil,
Thank you for the question. Changes in the volume of distribution may occur with different diseases, but I haven’t found a lot of research on the topic. There is one publication from 1976 on the topic that you may want to review (Klotz U., Pathophysiological and disease-induced changes in drug distribution volume: pharmacokinetic implications. Clin Pharmacokinet. 1976;1(3):204-18.). The change in volume of distribution depends on the type of disease and how that disease affects the physiology of the individual.

Comment on Understanding volume of distribution by Nabeil

Nabeil — Fri, 26 Apr 2013 06:50:04 +0000

please Mr Nathen how dose Vd change with disease