1 reply to this topic

[Jun Shen]

Hello,

 

Hope I am not asking too many questions. Here is one more. I want to do some user-defined calculation in differential equation system. Here is an example: calculate observed Cmax and model predicted Cmax

 

Originally, I have some code:

 

CC=DTA(7)

IF CC>Cm_OB THEN

  Cm_OB=CC

  Cm_Mod=Z(1)/Vc

ENDIF

 

DTA(7) is the column 7, where the concentration data is. After the program reads through all the data, Cm_OB is supposed to give me observed Cmax and Cm_Mod gives me the model predicted Concentration at the same time as the observd Cmax occurs. However I found Cm_Mod was not at the same time as the Cm_OB, which is assigned by CC.

 

I guess what happens is when CC reads a record, say at observed time 0.5 hour, the differential system has to start from zero. When Cm_OB=CC is executed, the system is still at somewhere between 0 and 0.5 hour, so Cm_Mod is the model predicted concentration sometime earlier than 0.5 hour.

 

My question is how I can synchronize Cm_OB and Cm_Mod. Thanks.

 

Jun

[Ana Henry]

Not sure this would help.

 

Initialize dta(3) to zero and make sire the first obs is t=0

Then use the code below and it will replace dta(3) with Cmax

The final cumulative Cmax will be on the output summary table – the code below was added to PK3 from Dan Weiner's PK/PD book

 

Model

COMM

  NCON 1

  NPAR 3

  PNAM 'VF','Tabs','Ke'

  NFUN 1

END

TEMP

  T = X

  DOSE = CON(1)

  FINF = DOSE/Tabs

END

 

transform

if x=0 then

  Cmax = y

endif

 

if x>0 and Cmax < y then

  Cmax = y

endif

 

dta(3)=Cmax

 

end

 

FUNC1

    F = 0.0

  IF T <= Tabs THEN

  F =(FINF/(Ke*VF))*(1. - DEXP(-Ke*T))

  ENDIF

  IF T > Tabs THEN

 F=(FINF/(Ke*VF))*(1.-DEXP(-Ke*Tabs))*DEXP(-Ke*(T-Tabs))

  ENDIF

END

EOM

 

------------ end ------------

Column3 is the first column below on the summary table

Cmax t Cp

0 0 0 0.0000 0.0000 0.0000 0.0000 1.0000 Missing Missing

10 0.5 10 0.5000 10.0000 20.3550 -10.3550 1.0000 1.3144 -1.8006

46 1 46 1.0000 46.0000 36.5204 9.4796 1.0000 2.0136 1.7097

56 1.5 56 1.5000 56.0000 49.3586 6.6414 1.0000 2.3729 1.2297

56 2 56 2.0000 56.0000 59.5544 -3.5544 1.0000 2.5967 -0.6711

66 3 66 3.0000 66.0000 74.0824 -8.0824 1.0000 3.1070 -1.6118

87 4 87 4.0000 87.0000 83.2454 3.7546 1.0000 3.8650 0.8425

87 5 69 5.0000 69.0000 69.3519 -0.3519 1.0000 5.2864 -0.1344

87 6 45 6.0000 45.0000 43.7414 1.2586 1.0000 3.0439 0.2491

87 7 29 7.0000 29.0000 27.5885 1.4115 1.0000 2.8880 0.2744

87 8 15 8.0000 15.0000 17.4005 -2.4005 1.0000 2.7040 -0.4579

87 9 10 9.0000 10.0000 10.9748 -0.9748 1.0000 2.3126 -0.1796

87 10 9 10.0000 9.0000 6.9220 2.0780 1.0000 1.8537 0.3711

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