Case study (gentamicin dosing & TDM)

We will now work through an example to show you how TDM can be used to optimise doses.

Please note that this case may not necessarily reflect actual clinical practices; it is merely intended to act as an exercise for you to calculate aminoglycoside dosing based on patient information and reflect on the role of TDM.

Case study

Mrs X, an elderly lady, presents to the hospital with an elevated serum creatinine level and urinary sepsis requiring Gentamicin therapy. Read on to find out more about her background and answer the following questions. Discuss your answers and chosen therapeutic approach in the comments section below.

You are encouraged to use your local guidelines for gentamicin dosing where available (if these are based on a 7 mg/kg once-daily regimen, then assume this is the intended dose for this case).

If you are unable to access local guidelines, then the following renal function estimation calculator may help you answer the questions.

When you’re finished, read through the Answers PDF available in downloads to compare your answers.

The doctor asks you to calculate the starting dose for her.

• What information do you need to know to calculate her starting dose?
• Calculate her creatinine clearance, using the formulas shown earlier in step 2.8
• What dose of gentamicin would you recommend based on this renal function?

21 hours later a post dose is taken, which comes back at 3.2mg/L.

• What type of level is this? Can the Urban and Craig nomogram be used to interpret the level?
• What would be your advice to the doctor?

Day 5 of treatment Mrs X is complaining of dizziness.

• Could this be a side effect of the gentamicin?
• Would you monitor for other signs of gentamicin toxicity?
• What would you monitor?

The microbiology department have authorised >5 days use. The patient is haemodynamically stable, as is their kidney function.

• How often should gentamicin levels be taken to monitor therapy?

Thank you for navigating through our case study, we hope you found it useful to apply what you have learnt to a more practical situation.

We have now reached the end of this weeks teaching, click next to move on and take a short quiz testing your knowledge of week 2.