ka_calculation_md: Calculate absorption rate constant (ka) in a multiple-dose...

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

Calculate absorption rate constant (ka) in a multiple-dose one-compartment model

Description

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

Usage

ka_calculation_md(cl, ke, t, Ct, Fbio = 1, Dose, tau)

Arguments

cl	Numeric. Clearance of the drug (in L/hr).
ke	Numeric. Elimination rate constant (in 1/hr).
t	Numeric. Time after the last dose (in hours) at which the concentration is measured.
Ct	Numeric. Observed concentration of the drug at time t (in mg/L).
Fbio	Numeric. Bioavailability fraction (default = 1, meaning 100% bioavailability).
Dose	Numeric. Administered dose of the drug (in mg).
tau	Numeric. Dosing interval (in hours) between successive doses.

Details

The value of ka is obtained numerically using the uniroot unction by solving the following equation:

Ct = \frac{Fbio \cdot Dose \cdot ka}{Vd \cdot (ka - ke)} \left( \frac{e^{-ke \cdot t}}{1 - e^{-ke \cdot \tau}} - \frac{e^{-ka \cdot t}}{1 - e^{-ka \cdot \tau}} \right)

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 the following components:

ka	The calculated absorption rate constant.
full_solution	The full solution object returned by the uniroot() function, which includes additional details about the root-finding process.

Author(s)

Zhonghui Huang

Examples

# Example from Oral_1CPT dataset (ID = 1, 5th dose, t = 2 h)
ka_calculation_md(cl = 4, ke = 0.057, t = 2, Ct = 852, Dose = 60000, tau = 24)

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