PharmPK Discussion - Estimating blood levels from plasma levels

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On 31 Aug 2000 at 10:34:51, "Micha Levi" (micha.aaa.umich.edu) sent the message


Dear Colleagues,

What would be the most accurate way to estimate blood levels of a compound
from its plasma levels. I can not determine the blood levels of the compound
directly in the blood.

Thank you,

Micha Levi
Graduate Student
The University of Michigan

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On 1 Sep 2000 at 15:29:56, David_Bourne (david.-at-.boomer.org) sent the message


[A couple of replies - db]

Sender: PharmPK.-a-.boomer.org
Reply-To: "Cotler, Stanley {NCDS~Nutley}" 
MIME-version: 1.0
From: "Cotler, Stanley {NCDS~Nutley}" 
Date:  Thu, 31 Aug 2000 21:45:31 -0400
To: david.aaa.boomer.org
Subject: Re: Estimating blood levels from plasma levels

If you know the blood to plasma ratio, can convert plasma values to blood
values
			Stanley Cotler

---

Sender: PharmPK.-a-.boomer.org
Reply-To: ml11439.-at-.goodnet.com (Michael J. Leibold)
Mime-Version: 1.0
From: ml11439.at.goodnet.com (Michael J. Leibold)
Date:  Fri, 1 Sep 2000 00:57:33 -0700 (MST)
To: david.at.boomer.org
Subject: Re: Estimating blood levels from plasma levels

The following message was posted to: PharmPK

Micha,

     One method of estimating drug concentrations in blood is to obtain
the drug concentration in red blood cells, and then calculate blood
concentrations from the following equation:

     C(blood)= C(rbc)*(HCT) + C(plasma)[1-HCT]

     C(rbc)= concentration in RBC's
     HCT= hematocrit

     The free fraction in the blood can be calculated as follows:

     Fb= (Fp)(Cp)/(Cb)

     Fb= free fraction in the blood
     Fp= free fraction in the blood
     Cp= concentration in the plasma
     Cb= concentration in the blood

                         Mike Leibold, PharmD, RPh
                         ML11439.at.goodnet.com

References
1)Gibaldi, M., Perrier, D., Pharmacokinetics, New York, Marcel Dekker
    1975
2) Gibaldi, M., Perrier, D., Pharmacokinetics 2nd ed, New York, Marcel Dekker
    1982

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On 13 Nov 2000 at 12:46:33, "Pugnaghi, Franca" (fp27373.-a-.GlaxoWellcome.co.uk) sent the message


I have new chemical entities with high erythrocytes binding  (EB >70%). Is
it better to measure blood levels instead of plasma? Or may I think to
correct plasma levels using the equations/ Is it better to measure in vivo
or in vitro erythrocytes partitioning?

Thank for your help
Franca

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On 20 Nov 2000 at 16:20:31, bvatul.at.ufl.edu sent the message


Franca
I think it would be better if whole blood is analysed
instead of plasma. You might characterise the terminal
phase in a much better way. It is better to measure
invivo binding but of course many parameters can be
better controlled in invitro studies.
Atul

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On 20 Nov 2000 at 16:20:41, "Ozlem Cukurlu" (Ozlem.-at-.medscape.com) sent the message


  Dear Franca,
I would rather measure blood levels of the new chemical entity you
are working on instead of measuring plasma levels and correcting them
with equations to see the results exactly the way they are. According
to the information you had gived working in vivo looks better but
what i think is that you need more information other than
erythrocytes binding to form your study in the right way ,according
to this information.

Hope this helps.

Ozlem Cukurlu
University Of Istanbul
Faculty of Pharmacy
Department of Pharmacology.

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On 20 Nov 2000 at 22:10:05, "Edward O'Connor" (edward.oconnor.-a-.Covance.Com) sent the message


probably best if you separated whole blood and plasma, then washe the
red cells with saline, then lysed them.  Red Cells and represent another
compartment within plasma.

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