This is a more advanced version of the previous interactive graph for dosage optimization. This interactive graph (loosely modelled after phenytoin) not only allows you to visualize the steady-state plasma concentration profile for a pre-selected pharmacokinetic profile, but allows you to randomly generate a fresh set of PK parameters based on the expected variability around the initial estimates for bioavailability, rate of absorption and volume of distribution.

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1. Select the pharmacokinetic parameters (rate of absorption, bioavailability and volume of distribution only) as close as you can to the drug of interest. The Vmax and Km for elimination is empirically preset to be 0.02 g/hr and 0.004 g/L, respectively. The half-life is not displayed as this is a non-linear model.

 

2. Define the maximum and minimum limits of the therapeutic range. (If you are not sure, just leave it blank. You can edit it later.)

 

3. Define the standard tablet size for this drug.

 

4. Then input your first dosage regimen, in terms of number of doses / dosing interval / number of tablets.

 

Sometimes, your first regimen gets the patient to the plasma concentration range required for optimal therapy. More often you will miss this range and will have to make dosage adjustments.

 

5. Amend the dosage regimen as often as you can by adding a new dosage regimen.

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Recognise that it is not often easy to achieve the desired concentration range. 

 

Note how long the process of optimization might take as you work towards each steady state. Note particularly how difficult it is to adjust the doses when the PK is non-linear.

 

Consider how you can improve the efficiency of this process.

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To check out the Linear PK version of this app, click here

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