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Tobramycin Dosing Regimen : Example 2

Tobramycin Dosing Regimen : Example 2
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11.1
Now based on the K ratio, we can also construct normal graph such as this. This is for specific for tobramycin. Percent of normal dosage. Creatinine clearance on the top. And the serum creatinine at the bottom. And It is a straight line. Therefore you can interpolate a dose for a specific kidney function. Let’s look at another example. This example says patient JT is 58 year old and 170 centimeter in height and the 58.3 kilo in weight. His serum creatinine is 2. What should be the loading dose as a percent of normal dose based on this half-life? Now, first you need to calculate the ideal body weight. And this is based on an equation that you can find from any pharmacokinetic textbook.
98.8
However, I simply give you the answer. The ideal body weight is 66 kilogram by the formula. Then estimate his creatinine clearance by Cock-croft equation which turns out to be 33 mL per minute. Again I will leave the detailed calculation to yourself. And then predict tobramycin half-life for this patient based on this specific formula which says ke is equal to 0.0024 times creatinine clearance plus 0.01. And the answer turn out to be half-life is equal to 7.7 hour. So if we read the next chart. We will find out that the uremic dose for this patient should be based on q8h should be about 50% of normal dose. And this is where you find the answer.
175.8
The first column creatinine clearance is 33. The second column the half-life is 7.7 hour. And then third column, therefore, the dose should be 50% of normal.

In this video, Prof. Lee demonstrates the steps to estimate the dosing regimen of Tobramycin.

To begin with, we can see that in the first diagram, the y-axis is the percent of normal dosage (%), and the x-axes are creatinine clearance (mL/min/1.73m2) and serum creatinine (mg/100mL).

Following that, we need to understand the steps to solve the question in the example: first, we should use the ideal body weight formula to get his IBW; secondly, estimate his creatinine clearance by C-G equation. Thirdly, predict the half-life of tobramycin for this patient.

Ultimately, we will read the dosing regimen from the table on the final slide.

Do you have any questions about the example2? Please leave them below.

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This content is taken from Taipei Medical University online course
Pharmacokinetics: Drug Dosing in Renal Disease
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