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TDM: Purpose & Examples : Tobramycin & Vancomycin

TDM: Purpose & Examples : Tobramycin & Vancomycin
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Now therapeutic drug monitoring very quickly. This slide that This cartoon says I stopped taking that medication because I prefer the original disease than the side effect. This is the cartoon but it tells you that the side effect could be unbearable for the patient. And the purpose of therapeutic drug monitoring is to adjust the plasma concentration to avoid the toxicity and to optimize or maximize the efficacy. Here we have one example. This was a very busy slide. However, I just want to make two points here. Here you have an ID specialist who placed this patient JT tobramycin therapy for Gram-negative sepsis, administrator as IV infusion 80 milligram q8h over 30 minutes.
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And of the time of infusion was scheduled at 7 a.m., 3 p.m, 11 p.m. On day 3 you as a pharmacist ordered two blood samples for therapeutic drug monitoring.
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One at 2:30 p.m.
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and the other at 4:30 p.m. So here the first column is a clock time. Second column is the event infusion. And the third column is elapsed time from the very beginning of infusion. And the last column is drug concentration for those two samples. The question that I have for you is why take those two samples at the corresponding time.
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And the answer is that one concentration the one at 2:30 p.m reflect the trough concentration.
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And the one at 4:30 p.m. reflect the maximum concentration. And the purpose of therapeutic monitoring is to maintain the therapeutic window. Maintain the concentration within the therapeutic window to maximize the effect yet to minimize the toxicity or side effect. So we performed therapeutic drug monitoring of aminoglycosides general for safety for effectiveness And in vulnerable patient population such as older patient or the patient on other nephrotoxic drug such as thiazide and other aminoglycoside. However, I need to remind you that please do not make clinical decisions on numbers alone. Another example for vancomycin. Now TDM of vancomycin is not appropriate if the patient received less than four doses.
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So we must wait for the patient to have received a minimum of three consecutive doses because of the long half-life of vancomycin and the sample should be obtained within 30 minutes of scheduled a dose. For example, just before the fourth dose or 30 minutes before the fourth dose. And target the trough concentration of 10 to 15 microgram per mL. And if there are no other risk factors then simply monitored serum concentration every 3 to 5 days.

In this step, Prof. Lee illustrates the purpose of Therapeutic Drug Monitoring (TDM), and gives examples for different drugs.

To begin with, we know that the side effect could be unbearable for the patient. Thus, the purpose of therapeutic drug monitoring is to adjust the plasma concentration to avoid the toxicity and to optimize or maximize the efficacy.

Secondly, we can learn to distinguish the peak and the trough concentration from the table in the TDM example for Tobramycin.

Besides, there are some important hints. When we use TDM on Aminoglycosides, do not make clinical decisions on numbers alone.

Finally, we should notice that the target trough of Vancomycin is between 10 and 15 ug/ml, depending on the patient’s situation.

Have you completed any TDM before? What was the target trough of Vancomycin ? If possible, you can share which country you’re in as well.

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