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This is in response to the letter by Grant and Macdonald on medicines for children and gentamicin toxicity in Archives of Disease in Childhood.1
Recently we audited our gentamicin regimen (2.5 mg/kg/dose; 24 hourly for < 29 week postconceptional age (PCA); 18 hourly for 29–35 week PCA; 12 hourly for > 35 week PCA) because of concerns that it resulted in too many subtherapeutic peak levels. We prospectively audited 50 sets of levels. Trough levels were determined just before and peak levels one hour after the third dose. Desired levels were trough < 2 μg/ml and peak 5–10 μg/ml. Most of the peak levels (92%; 46/50) were < 5 μg/ml. Trough levels were < 2 μg/ml in 98% (49/50). During the study period, 108 sets of levels were analysed by the microbiology department. A peak level of < 5 μg/ml was noted in 100/108, and a trough level of < 2 μg/ml in 107/108.
We changed our gentamicin regimen (4 mg/kg/dose; 36 hourly for < 28 week PCA; 24 hourly for ⩾28 week PCA; trough levels determined before the third dose and peak levels not determined routinely), guided by current evidence,2–5 and prospectively reaudited 60 levels. We randomly determined 20 peak levels; these were in the range 5.8–7.5 μg/ml in 16/20. Trough levels were < 2 μg/ml in 97% (58/60). During this study period, 100 trough levels were analysed in total, and only 4/100 were ⩾2 μg/ml, the highest being 2.3 μg/ml.
We are happy with our new gentamicin regimen as it is practical and easy to remember. It achieves therapeutic levels without any added risk of toxicity. We have stopped routinely determining peak levels, resulting in less trauma and blood sampling for delicate newborns and the saving of laboratory time. The decision to not determine peak levels routinely is based on current evidence2–5 that a dose of 4 mg/kg is highly likely to give peak levels in the desired range. Discretion, however, will have to be used in clinically septic newborns. In the long run, it should result in significant cost savings, as analysing the gentamicin levels has been reported to represent 75% of the cost of using this relatively inexpensive drug.4