# Absorption delay

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### #1 jangjh0121

jangjh0121

Newbie

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• 1 posts

Posted 06 July 2020 - 09:06 AM

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 Simon Davis

Simon Davis

• 1,129 posts

Posted 13 July 2020 - 11:13 AM

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

gamma distribution is not the same as Weibull, see here; https://en.wikipedia...ma_distribution
https://en.wikipedia...ll_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)

Edited by Simon Davis, 14 July 2020 - 09:44 AM.
added Gamma shape reference

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