Bioequivalence and Bioavailability Forum • Vss

Vss [PK / PD]

posted by d_labes – Berlin, Germany, 2011-10-18 13:36 (5359 d 12:20 ago) – Posting: # 7512
Views: 25,001

Dear Martin!

The TOPFIT2.0¹⁾ manual states (in the non-compartmental section):
"Estimation of Vss is only possible following intravenous administration because:
a) the bioavailability factor f is unknown following oral administration and
b) the intrinsic MRT is needed (the intrinsic MRT is the MRT of the substance within the systemic circulation and thus corresponds to the MRT calculated from plasma data only in the case of intravenous administration)."
(Emphasis by me)

Formulas given:
iv-bolus
Vss = CL * MRT
iv-infusion

  Vss = CL * (MRT - IT/2)

      = CL * MRT_intr

where CL is the clearance, IT the infusion time and MRT_intr=MRT of disposition disregarding the infusion time.

If I remember the old days I had done compartmental modelling right the p.o. MRT is something like
MRT_po = MRT_iv + 1/k_a + t_lag
in the one-compartmental model.

Hope this helps.

¹⁾Heinzel, Woloszczak, Thomann
"TopFit 2.0
Pharmacokinetic and Pharmacodynamic Data Analysis System for the PC"
Gustav Fisher Verlag, Stuttgart-Jena-New York 1993

—
Regards,

Detlew

Complete thread:

volume of distribution at steady state martin 2011-10-18 07:49
- Vssd_labes 2011-10-18 11:36
  - History Helmut 2011-10-18 16:02
    - History javier 2016-09-21 16:47
      - Amazon? Yes. yjlee168 2016-09-22 11:30
        
        Gold Letters d_labes 2016-09-22 12:09
        
        Gold Letters yjlee168 2016-09-24 20:26
        
        Another quest mittyri 2016-09-25 15:04
        
        TopFit: 16bit DOS-application Helmut 2016-09-25 23:41
        
        TopFit: less than 1.44 MB mittyri 2016-09-26 00:02
        
        TopFit: less than 1.44 MB Helmut 2016-09-26 00:17
        
        TopFit: less than 1.44 MB ElMaestro 2016-09-26 09:43
        
        TopFit: 16bit DOS-application yjlee168 2016-09-26 00:18
- volume of distribution at steady state ElMaestro 2016-09-23 23:13
  - Vss: MIT is needed anyway... mittyri 2016-09-24 00:38
    - it seems possible for me... yjlee168 2016-09-24 20:19
      - Leslie disagrees mittyri 2016-09-24 21:33
        
        OK! we cannot calculate Vdss with dataset from extravascular dosing alone yjlee168 2016-09-25 23:27
        
        MRTINF includes Mean Input Time mittyri 2016-09-25 23:45
        “Gravity Duration” Helmut 2016-09-25 23:47
    - Was Leslie wrong about Eq (8)? yjlee168 2016-09-26 00:13
      - Leslie cannot be wrong mittyri 2016-09-26 00:23