# Module 3.5: OneCompartAspirin

If the above applet fails to run you can launch Nova using Java Web Start.

### To run this model on your version of Nova click here to download
and save its file.

This model shows a simplified version of the way the body processes a
drug, in this case, aspirin. This model assumes that the body is one
homogenous compartment with instantaneous drug distribution, hence
one-compartment.

The green box is the stock that represents the mass of the aspirin
that's immediately available in the plasma. Its initial value is the
mass of two aspirin: 2 pills * 325 mg * 1000 μg/mg, the conversion
factor to μg. The flow from aspirin in plasma represents
elimination. It is proportional to the amount of aspirin in plasma,
times an elimination constant, which is represented as a pink circular
term. The rate of change of the drug leaving the system is
proportional to the quantity of the drug in the system.

Let's take a closer look at what components go into elimination. The
elimination constant has a red arrow going to it from the pink term
"half life." In this model, the half-life is estimated at 3.2
hours. The relationship between the elimination constant and the
drug's half-life is shown in Nova with the following equation: -
Math.log(.5)/half_life.

The output from this model is shown as a graph of the term plasma
concentration, which shows the amount of aspirin in plasma divided by
the plasma volue, 3000 ml. The graph shows that the concentration of
aspirin in the plasma is initially around 217 μg/ml, then decreases
exponentially.