• Gentamicin is an antibiotic used to treat serious bacterial infections.
• It is important that you take enough of the drug to kill the bacteria but not too much that it causes serious side effects.
• This balance is achieved by regularly monitoring levels of the drug in your blood.
• This is usually done at the time just before your next dose. This is called the tough level. If needed, your dose can be adjusted.

Gentamicin is an antibiotic that is used to treat serious bacterial infections. It belongs to a group of antibiotics called aminoglycosides.

These infections are often caused by gram-negative or gram-positive bacteria. For more see Gram stain.

Gentamicin is used for serious infections for which other antibiotics may not work. It is given given as an injection often over many weeks depending on the level of infection.

If you are given too much gentamicin, it can cause toxic side-effects, including damage to your hearing and/or balance as well as acute kidney damage. On the other hand, gentamicin will not work if there is not enough in your body to kill the bacteria that is causing the infection. For this reason, a balance must be found to achieve the right dose. Too much and there is a risk of side-effects and too little and there is less chance of the bacteria being killed.

To achieve this balance your dose may need to be monitored and adjusted to reduce the risk of side effects. Your doctor will ask for regular blood tests to make sure the gentamicin levels remain within a safe range. They may use therapeutic drug monitoring (TDM) to tailor the dosage specifically for you.

Monitoring your dose

When you have a gentamicin injection the level rises in your blood to a peak concentration and then falls over time to a lower concentration called the trough level. The trough level is the minimum amount of gentamicin in your blood before the next does is given.

Gentamicin may be monitored in different ways but one of the more common ways is to measure the trough level and use this to guide whether the next dose needs to be adjusted up or down.

Each of us responds to medications in different ways. Some people may take time to clear gentamicin from their body. For example, if you are elderly or have an underlying condition such as kidney disease. This results in a higher concentration of gentamicin in the blood, with the risk of serious side effects. So, the dose you are given might be lower than the one you had previously or else you may be asked to have the drug less often.

If your trough level is found to be too low, with the risk that the bacteria will continue to survive in your body, your dose may be increased, or the drug may be given more often.

Monitoring may become less frequent when your gentamicin results are in the desired range and there are no clinical signs that indicate that the levels may not be right.

Another reason for the importance of monitoring is that other medications may be prescribed in addition to gentamicin. These medications may affect how your body deals with gentamicin by either increasing the risk of side effects or reducing its effectiveness. Monitoring trough levels will show if they are having any effect and whether your dose needs to be adjusted.

It is important to tell your doctor about all of the medications you are taking so the gentamicin dose can adjusted as required.

Sample

Blood

Any preparation?

No test preparation is needed, but the timing of the blood sample is important.

Reading your test report

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

The trough level of gentamicin guides your doctor on whether your dose of the drug of the frequency it is given needs to be adjusted.

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods, medications or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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