Absorption delay

Phoenix Certara Forums Modelling and Simulation
1

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

2

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)