Compute the half-life and associated parameters

The terminal elimination half-life is estimated from the final points in the concentration-time curve using semi-log regression (log(conc)~time) with automated selection of the points for calculation (unless manually.selected.points is TRUE).

pk.calc.half.life(
  conc,
  time,
  tmax,
  tlast,
  manually.selected.points = FALSE,
  options = list(),
  min.hl.points = NULL,
  adj.r.squared.factor = NULL,
  conc.blq = NULL,
  conc.na = NULL,
  first.tmax = NULL,
  allow.tmax.in.half.life = NULL,
  check = TRUE
)

Arguments

conc	Concentration measured
time	Time of concentration measurement
tmax	Time of maximum concentration (will be calculated and included in the return data frame if not given)
tlast	Time of last concentration above the limit of quantification (will be calculated and included in the return data frame if not given)
manually.selected.points	Have the points being input been manually selected? The impact of setting this to `TRUE` is that no selection for the best points will be done. When `TRUE`, this option causes the options of `adj.r.squared.factor`, `min.hl.points`, and `allow.tmax.in.half.life` to be ignored.
options	List of changes to the default `PKNCA.options` for calculations.
min.hl.points	The minimum number of points that must be included to calculate the half-life
adj.r.squared.factor	The allowance in adjusted r-squared for adding another point.
conc.blq	See `clean.conc.blq`
conc.na	See `clean.conc.na`
first.tmax	See `pk.calc.tmax`.
allow.tmax.in.half.life	Allow the concentration point for tmax to be included in the half-life slope calculation.
check	Run `check.conc.time`, `clean.conc.blq`, and `clean.conc.na`?

Value

A data frame with one row and columns for

tmax

Time of maximum observed concentration (only included if not given as an input)

tlast

Time of last observed concentration above the LOQ (only included if not given as an input)

r.squared

coefficient of determination

adj.r.squared

adjusted coefficient of determination

lambda.z

elimination rate

lambda.z.time.first

first time for half-life calculation

lambda.z.n.points

number of points in half-life calculation

clast.pred

Concentration at tlast as predicted by the half-life line

half.life

half-life

span.ratio

span ratio [ratio of half-life to time used for half-life calculation

Details

If manually.selected.points is FALSE (default), the half-life is calculated by computing the best fit line for all points at or after tmax (based on the value of allow.tmax.in.half.life. The best half-life is chosen by the following rules in order:

At least min.hl.points points included
A lambda.z > 0
The best adjusted r-squared (within adj.r.squared.factor)
The one with the most points included

If manually.selected.points is TRUE, the conc and time data are used as-is without any form of selection for the best-fit half-life.

References

Gabrielsson J, Weiner D. "Section 2.8.4 Strategies for estimation of lambda-z." Pharmacokinetic & Pharmacodynamic Data Analysis: Concepts and Applications, 4th Edition. Stockholm, Sweden: Swedish Pharmaceutical Press, 2000. 167-9.