## Zero order helps often [Regulatives / Guidelines]

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.

Dif-tor heh smusma 🖖 Довге життя Україна!
Helmut Schütz

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