Absorption delay

Dear all,

I am a novice and trying to apply various absorption models to population PKs.

Among the NLME example files, there is a file related to absorption delay (ModelAbsorptionDelay_delayInfCpt.phxproj).

I want to know what the shapeparameter and meandelaytime mean in the formula. Does the gamma distribution assumed here mean the Weibull distribution?

Jang

Hi Jang, if you look at ‘model’ in Setup tab you will see the code is annotated.

and the online help describes more about this code; https://onlinehelp.certara.com/phoenix/8.3/index.html#t=topics%2FDiscrete_and_distributed_delays.htm&rhsearch=ShapeParamMinusOne

gamma distribution is not the same as Weibull, see here; https://en.wikipedia.org/wiki/Gamma_distribution
https://en.wikipedia.org/wiki/Weibull_distribution

===============================================================================

/*
Assumptions on the model

  • One compartment model with 1st-order clearance
  • The delay time between the administration time of the drug
    and the time when the drug molecules reach the central compartment
    is assumed to be gamma distributed with mean = MeanDelayTime and
    shape parameter being (ShapeParamMinusOne + 1)
    */

================================================================================

central compartment

delayInfCpt(A1, MeanDelayTime, ShapeParamMinusOne, out = - Cl * C, dist = Gamma)
dosepoint(A1)

drug concentration at the central compartment

C = A1 / V

============== residual error model ===================================================

error(CEps = 0.1)
observe(CObs = C * (1 + CEps))

============== Model parameters =========================================================

------------ structural model parameters ---------------------------------------------

stparm(V = exp(tvlogV + nlogV)) # volume of distribution for central compartment
stparm(Cl = exp(tvlogCl + nlogCl)) # central clearance
stparm(MeanDelayTime = exp(tvlogMeanDelayTime + nlogMeanDelayTime)) # mean delay time
stparm(ShapeParamMinusOne = exp(tvlogShapeParamMinusOne)) # (ShapeParameter - 1)