7/21/2019 Medication Model

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System Dynamics (VenSim) Challenge: Apprenticeship Level 1

Simulating Therapeutic Medication Levels

Background Reading

Dr. Brocket practices internal medicine in a maor So!th "astern city. #ne day $s.

%omes came in &or a check!p and descri'ed the symptoms o& a serio!s kidney condition.

he medication that is !sed to treat her kidney condition isnt e&&ective !ntil the patienthas at least 1** milligrams in her 'ody. +& the medicine level reaches a'ove ,**

milligrams- it 'ecomes toic to the 'ody. he 'ody meta'oli/es ('reaks do0n) and

ecretes this medication at a rate o& 1* o& the amo!nt in the 'ody every ho!r. Dr.

Brocket needs to prescri'e the medication in the proper dosage so $s. %omes 0ill get0ell and not have harm&!l side e&&ects &rom an overdose.

Certification Challenge

 2o!r task is to constr!ct a VenSim model that 0ill prod!ce the graph 'elo0 and help Dr.

Brocket &ind a dosage rate that is sa&e- e&&ective and convenient &or $s. %omes to takedaily.

3e are interested in the val!es held in the &ollo0ing reservoir: 1.$edication level

At the 'eginning o& the model- the medicine level reservoir contains these val!es:

1. $edication Level: *

4or the medication reservoirs- here is a description o& the in&lo0s and o!t&lo0s:1. $edication Level: he medication reservoir has 5 rates- one coming in and one

  going o!t.

A. ake pills: an in&lo0 (a 6rate7 in VenSim notation). he take pills

in&lo0 depends on 8 a!iliary varia'les:

i. Start taking: this is the time it takes $s. %omes to get her prescription &illed and take her &irst dose. Set the initial val!e to

,.

ii. ime 'et0een dosages: this is the n!m'er o& ho!rs $s. %omes0aits 'et0een dosages. Set the initial val!e at 5, or once a day.

iii. Dosage: this is the n!m'er o& mg o& medicine that $s. %omes

takes 0ith each dose. Set the initial val!e at 5**.he &orm!la in take pills is 9 ;LS" <A+=( >start?start taking -

>d!ration?*.5@- >repeattime?time 'et0een dosages - >end?1** )dosage.

he d!ration is set to *.5@ the time step. he end is set to 1** ho!rs the

end o& the sim!lation.

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B.

"creted: an o!t &lo0. "creted depends on the a!iliary varia'le

ecretion rate. he ecretion rate is set at .1 or 1*. he &orm!la inecreted is9 $edication levelecretion rate.

here are 5 other important &actors:

1. herape!tic level: an a!iliary varia'le set at 1**.

5. oic level: an a!iliary varia'le set at ,**.

he time !nit &or this model is ho!rs- and 0e 0ant to r!n it &rom * to 1** ho!rs or !st

over , days. 2o!r time step sho!ld 'e set to .5@. 2o!r model sho!ld have:

1 'o varia'le

5 rates a!iliary varia'les

@ connectors

3hen yo! r!n yo!r model- it sho!ld prod!ce a graph that looks like the one 'elo0:

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