Bioequivalence and Bioavailability Forum

Hi PharmCat,

❝ I can be wrong.

No, you aren’t.

❝ I suppose when we have modified release dosage form there are can be some changes in the PK model. […] So resulting PK profile can be wery surprising.

In many cases a good model is similar to an infusion (i.e., zero order input). The only difference is that instead of the length of the infusion \(t_\textrm{i}\) the end of absorption \(t_\textrm{e}\) is used:
$$C(t)=\frac{f\; D}{t_\textrm{e}\; V\; k_\textrm{el}}\left [\exp (k_\textrm{el}\cdot t^{*})-\exp (k_\textrm{el}\cdot t) \right ]\left\{\begin{matrix}
t>t_\textrm{e} \to t^{*}=t-t_\textrm{e}\\
t\leqslant t_\textrm{e} \to t^{*}=0
\end{matrix}\right.$$Little bit tricky cause \(t_\textrm{i}\) is a known constant and \(t_\textrm{e}\) and estimate.