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# Keywords to use administration information

## Time-related keyword

The reserved keyword for the time is t. It corresponds to the time defined in the TIME column in Monolix, and the times defined in the treatment, observation and regressor elements in Simulx.

Example:

The keyword time can be used to define a time-varying clearance for instance:

[LONGITUDINAL]
input = {V, CLini, CLss, T12}

EQUATION:
Cl = CLss - (CLss-CLini)*exp(-t/T12)
Cc = pkmodel(V,Cl)

Information related to the doses defined in the data set or in the Simulx treatment elements are available in the structural model via several keyword. They are piece-wise constant functions which value is updated each time there is a dose. Before the first dose, their value is zero.

The value of the keyword are directly related to the design, they are unaffected by the absorption/depot macros  arguments such as Tlag or p. Note that doses are not discriminated according to their administration types.

• tDose: holds the time of the last administered dose.
• amtDose: holds the amount of the last administered dose.
• inftDose: holds the infusion duration of the last administered dose.

Example:

The keyword amtDose can be used to define a dose-dependent absorption for instance:

[LONGITUDINAL]
input = {ka, V, Cl, D50}

EQUATION:
F = D50/(amtDose+D50)
Cc = pkmodel(ka, V, Cl, p=F)