halflife {linpk}

Half-lives of a linear PK system.

Description

Half-lives of a linear PK system.

Usage

halflife(x)

Arguments

x

A object of class pkprofile.

Value

A numeric vector containing the half-lives for the different phases of the system. The number of phases generally equal the number of compartments, plus one for the absorption phase if the system has first order absorption (i.e. if ka is specified). The values are returned sorted in ascending order, so the first corresponds to the alpha phase, the second beta, the third gamma, and so on. The absorption half-life, if present, comes last (it can also be identified by comparing it to the value of log(2)/ka).

Examples

y <- pkprofile(0, cl=0.25, vc=5, ka=1.1)
halflife(y)
log(2)/1.1

y <- pkprofile(0, cl=0.25, vc=5, ka=0.01)  # Flip-flop kinetics
halflife(y)
log(2)/0.01

# Three-compartment model
y <- pkprofile(0, cl=2, vc=10, q=c(0.5, 0.3), vp=c(30, 40))
halflife(y)

# The terminal half-life can be used to obtain the terminal slope of the
# concentration-time curve on the semi-log scale:
t.obs <- seq(0, 36, 0.1)
y <- pkprofile(t.obs, cl=0.25, vc=5, ka=1, dose=list(t.dose=0, amt=1))
plot(log2(y))
abline(-2.247927, -1/halflife(y)[1], col=adjustcolor("blue", 0.2), lwd=12)