# RE: Variability on infusion duration

From: Bill Denney <wdenney>
Date: Wed, 5 Aug 2020 13:38:14 -0400

Similar to Leonid's solution, you can try using an exponential distribution=
:

D1 = DUR*(1-EXP(-EXP(ETA(1))))

The exponential within an exponential gives left skew and ensures that D1 =

DUR.

For subjects who you know had an incomplete infusion duration, I would add
an indicator variable (1 if incomplete, 0 if full duration) so that the
subjects with complete duration have the known complete duration.

D1 = DUR*(1 - Incomplete*EXP(-EXP(ETA(1))))

Thanks,

Bill

-----Original Message-----
From: owner-nmusers
Of Leonid Gibiansky
Sent: Wednesday, August 5, 2020 12:51 PM
To: Patricia Kleiner <pklei05
Subject: Re: [NMusers] Variability on infusion duration

may be
D1=DUR*EXP(ETA(1))
IF(D1.GT.DocumentedInfusionDuration) D1=DocumentedInfusionDuration

On 8/5/2020 12:18 PM, Patricia Kleiner wrote:
> Dear all,
>
> I am developing a PK model for a drug administered as a long-term
> infusion of 48 hours using an elastomeric pump. End of infusion was
> documented, but sometimes the elastomeric pump was already empty at
> this time. Therefore variability of the concentration measurements
> observed at this time is quite high.
> To address this issue, I try to include variability on infusion
> duration assigning the RATE data item in my dataset to -2 and model
> duration in the PK routine. Since the "true" infusion duration can
> only be shorter than the documented one, implementing IIV with a
> log-normal distribution
> (D1=DUR*EXP(ETA(1)) cannot describe the situation.
>
> I tried the following expression, where DUR ist the documented
> infusion
> duration:
>
> D1=DUR-THETA(1)*EXP(ETA(1))
>
> It works but does not really describe the situation either, since I
> expect the deviations from my infusion duration to be left skewed. I
> was wondering if there are any other possibilities to incorporate
> variability in a more suitable way? All suggestions will be highly
> appreciated!
>
>
> Thank you very much in advance!
> Patricia
>
>
>
Received on Wed Aug 05 2020 - 13:38:14 EDT

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