Dosage adjustment and further monitoring

The target levels that are being aimed for can vary between different healthcare providers.

In a previous step, we provided a table of recommendations given by the Bristol Reference Laboratory (you can access this table again at the bottom of this step in the ‘downloads’ section).

Levels for gentamicin can be interpreted as follows:

1. Once a plasma level result is available if taken correctly between 6 – 14 hours after the gentamicin infusion, clinicians use the concentration of gentamicin measured in the plasma and the time after the start of the infusion of the sample to see where this point lies on the Urban and Craig nomogram, which shows if any changes in dosing interval are necessary.
2. If this time window is missed and a level taken between 18 – 24 hours is greater than 1mg/L, clinicians should request that a level be repeated 12 hours afterwards before any further doses are given. Once the level has dropped to below 1mg/L, dosing can be restarted at a frequency recommended by the nomogram.
3. If patients are clinically stable with normal kidney function, levels continue to be measured twice a week. Less stable patients with poor kidney function will have plasma levels measured more often.

Often monitoring can be more complex than this as patients may miss doses, may be given a dose later than scheduled or levels may be difficult to obtain or interpret for other reasons described in the previous step. It is always a good idea to repeat a level if interpretation is difficult and to seek expert advice if this is the case.

Accurate monitoring practices are essential to keeping the patient safe from toxicity.

In the final part of this activity on TDM, you will be able to navigate through our case study to learn more about how TDM is used in practice.