Calculating AUC at steady state

[Amy Moody]

Hi,

I want to calculate AUC only over the last 24 hours of dosing to capture the AUC of steady state drug concentrations. In other programs, the simulation stop time is passed to the model. I then set up an IF statement so that concentration is only captured during the last 24 hours. How can this be done in IQRtools? Are there variable names that refer to the current time and stop time? 

Thanks,

Amy

[Henning Schmidt]

Hi Amy,

you can do this in several ways. Will list some of them in the order of my personal preference:

Option 1: Similar to Option 2 but with a fine grid. Example: simtime = seq(0,240,0.1). Then averaging over CONC readouts in the last 24 hours and multiplying by 24. Not as numerically correct as Option 1 but for practical purposes with fine enough grid OK.

Option 2: I use a defined simulation time vector. Example: simtime = seq(0,240,24) (let's assume a 24 hour dosing interval). In the model I have d/dt(AUC) = Conc. From the simulation results I take the difference of the AUC variable. The last value is the AUC over the last 24 hours.

Option 3: As in option 1 you can have a state d/dt(AUC) = CONC. Using the even construct you can reset AUC to 0 at defined times or for defined conditions. For equidistant dosing (e.g. 24 hours) you could define an event as follows:

myeventname = eq(mod(time,24),0),AUC,0

Then at the end of each 24 hour interval AUC would contain the value of the AUC in this interval.

A very simple example model for Option 3 is below this email. No dosing here ... just some trajectory and calculating AUC in 24 hour increments.

There are more possibilities to do this ... but Option 1 is the one I typically use.

Cheers,

Henning

********** MODEL NAME
Provide Model Name
********** MODEL NOTES
Provide Model Information
********** MODEL STATES
d/dt(CONC) = -0.001*CONC
d/dt(AUC) = CONC
CONC(0) = 100
********** MODEL PARAMETERS
********** MODEL VARIABLES
********** MODEL REACTIONS
********** MODEL FUNCTIONS
********** MODEL EVENTS
myeventname = eq(mod(time,24),0),AUC,0

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[Amy Moody]

Thank you. Just taking the difference of the AUC is very easy, probably should have realized that option.

Amy