calculate_vd: Calculates volume of distribution from concentration data

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

Calculates volume of distribution from concentration data

Description

Calculates the volume of distribution (Vd) using an adaptive single-point approach

Usage

calculate_vd(
  dat,
  half_life = NULL,
  dose_type = NULL,
  pooled_ctrl = pooled_control(),
  route = c("bolus", "oral", "infusion")
)

Arguments

dat	A data frame containing raw time–concentration data in the standard nlmixr2 format.
half_life	Optional numeric value for the drug's half-life. If not provided, it will be estimated using get_hf() from pooled observations.
dose_type	Specifies the dosing context of the pharmacokinetic observations. Required when half_life is not provided. Classified as first_dose, repeated_doses, or combined_doses based on whether observed concentrations occur following the first administration, during repeated dosing, or across both contexts.
pooled_ctrl	Optional list of control parameters used by get_pooled_data() for pooling observations. Defaults to output from pooled_control().
route	Character string specifying the route of administration. Must be one of bolus, oral, or infusion. Currently, oral is not implemented.

Details

The function uses a concentration observed within the first 20% of the elimination half-life after dosing as the early point for estimating the volume of distribution.

Vd = \frac{\text{Dose}}{C_0}

For infusion:

Vd = \frac{\text{Rate} \times \min(\text{TIME}, \text{durationobs})}{C_0}

Here, C_0 represents the early concentration observed within the first 20% of the elimination half-life after dosing, which is used as an approximation of the initial concentration for estimating volume of distribution (Vd). TIME refers to time after dose; durationobs is the actual infusion duration.

When half_life is not provided, it is estimated from pooled data using the functions get_pooled_data() and get_hf().

Value

A list with two elements:

• vd_df: individual volume of distribution estimates

• trimmed_mean_vd: population volume of distribution estimated as a trimmed geometric mean using a 5 percent trimming level

Author(s)

Zhonghui Huang

See Also

get_pooled_data, get_hf, trimmed_geom_mean

Examples

dat <- Bolus_1CPT
out <- processData(dat)
fdat<- out$dat
froute <-out$Datainfo$Value[out$Datainfo$Infometrics == "Dose Route"]
half_life <- get_hf(dat = fdat)$half_life_median
calculate_vd(dat = fdat, half_life = half_life,route=froute)$trimmed_mean_vd

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