## 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 (

$$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.

» 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.

—

Helmut Schütz

The quality of responses received is directly proportional to the quality of the question asked. 🚮

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*Dif-tor heh smusma*🖖Helmut Schütz

The quality of responses received is directly proportional to the quality of the question asked. 🚮

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### Complete thread:

- EMA: Waiving MD study Helmut 2020-09-09 16:21 [Regulatives / Guidelines]
- EMA: Waiving MD study wienui 2020-09-09 17:43
- EMA: Waiving MD study Helmut 2020-09-09 19:26

- PK model PharmCat 2020-09-10 20:12
- Zero order helps oftenHelmut 2020-09-10 22:26
- Zero order helps often PharmCat 2020-09-11 02:33
- Distributed delay mittyri 2020-09-11 05:31

- Zero order helps often PharmCat 2020-09-11 02:33

- Zero order helps oftenHelmut 2020-09-10 22:26

- EMA: Waiving MD study wienui 2020-09-09 17:43