absorption / elimination [PK / PD]

posted by Helmut Homepage – Vienna, Austria, 2017-04-26 11:26  – Posting: # 17266
Views: 1,779

Hi VSP,

» Can we define the absorption phase and elimination phase with concentration time data/Plot?

[image]There is no “absorption/elimination phase”. Both absorption / elimination start almost immediately with dosing. See here (ka > kel) and there (ka = kel; flip-flop PK).

As long as drug is released from the formulation and dissolved, absorption continues untilIf you are interested in λz (as an estimate of kel) consider the TTT-method (see this post). At the inflection point of the profile (2×tmax) absorption is practically (!) complete (i.e., 93.75%).

 i    % abs.
0.5   50.00
1     75.00
1.5   87.50
2     93.75
2.5   96.875
3     98.4375
3.5   99.21875
4     99.609375

where i is the multiplier of tmax. Once you have an estimate of elimination you can obtain absorption f.i. by the method of residuals or by Wagner-Nelson’s.

Cheers,
Helmut Schütz
[image]

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