Gent peak/trough

The desired peak serum concentration of gentamicin is 5 to 12 mg/L,. The appropriate adjustment for a  peak serum concentration that is higher than the desired range is to decrease the dose of  the antibiotic.

Furosemide has no role in the treatment of gentamicin overdosage or toxicity. In fact, the addition of furosemide increases the potential risk of oto- and nephrotoxicity.  

The desired trough serum concentration of gentamicin is 0.5 to 1.0 mg/L, and the  concentration reported for the infant in the vignette is within that desired range. Therefore,  no adjustment in the dosing interval is warranted.

The pharmacokinetics, antimicrobial profile, and adverse effects of tobramycin are similar to those of gentamicin. Replacing one aminoglycoside with another is unlikely to  be of any benefit.

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Pediatric Pharmacology: Therapeutic Principles in Practice. 2nd ed.
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de Hoog M, Schoemaker RC, Mouton JW, van den Anker JN. Tobramycin
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Hayani KC, Hatzopoulos FK, Frank AL, et al. Pharmacokinetics of
once-daily dosing of gentamicin in neonates. J Pediatr. 1997;131:78-80