ka_calculation_sd: Estimate absorption rate constant in a one-compartment oral...

In nlmixr2autoinit: Automatic Generation of Initial Estimates for Population Pharmacokinetic Modeling

Estimate absorption rate constant in a one-compartment oral model

Description

This estimates the absorption rate constant in a single-dose oral model using first-order pharmacokinetics.

Usage

ka_calculation_sd(cl, ke, t, Ct, Fbio = 1, Dose)

Arguments

cl	Numeric. Clearance of the drug.
ke	Numeric. Elimination rate constant.
t	Numeric. Time after administration.
Ct	Numeric. Observed plasma concentration at time t.
Fbio	Numeric. Absolute bioavailability fraction. Default is 1.
Dose	Numeric. Administered oral dose.

Details

The model assumes a one-compartment structure with first-order absorption and first-order elimination.

The concentration-time relationship is:

Ct = \frac{Fbio \cdot Dose \cdot ka}{Vd \cdot (ka - ke)} \left( e^{-ke \cdot t} - e^{-ka \cdot t} \right)

where the volume of distribution is defined as:

Vd = \frac{cl}{ke}

ka is estimated using uniroot(), which solves for the root of the residual function (predicted Ct - observed Ct) within a bounded interval (ka > ke and ka <= 1000)

Value

A list containing:

ka	Estimated absorption rate constant.
full_solution	The full result object returned by the root-finding process.
message	A character string indicating the status of the estimation or any warnings.

Author(s)

Zhonghui Huang

Examples

# Example from Oral_1CPT dataset (ID = 1, 1st dose, t = 0.5 h)
ka_calculation_sd(cl = 3.62, ke = 0.0556, t = 0.5, Ct = 310.6, Dose = 60000)

nlmixr2autoinit documentation built on Nov. 14, 2025, 1:07 a.m.