lag-time – another round [Design Issues]

posted by Helmut Homepage – Vienna, Austria, 2024-10-19 10:20 (15 d 14:42 ago) – Posting: # 24242
Views: 493

Hi Titus,

❝ But clearly in the plot, there is no significant lag time.

You wrote the model without one…

❝ I believe, lag-time can be only observed in normal Conc-time plot. Isn't?

Depends on what you mean by ‘observe’.
By convention in NCA BQLs before tmax are set to zero. Of course, 0 cannot be shown in a log-linear plot. By another convention, tlag is defined as the time point before the first measurable concentration. Obviously that’s not correct (see also there). The true one is a little later. Another approach1 is not implemented in any software; roll out your own code. Of course, you can estimate tlag by a PK model.2


  1. Csizmadia F, Endrényi L. Model-Independent Estimation of Lag Times with First-Order Absorption and Dis­po­sition. J Pharm Sci. 1998; 87(5): 608–12. doi:10.1021/js9703333
  2. In all exponential functions substitute \(\small{t}\) by \(\small{(t-t_\text{lag})}\) with the fitting constraint \(\small{t_\text{lag}\ge 0}\).

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