Clinical Significance

Tobramycin is an aminoglycoside antibiotic whose in vitro activity is similar to that of gentamicin against gram negative bacteria. It has a higher activity against pseudomonas. Strong correlations have been shown between serum levels and both therapeutic effect and toxicity in specific patient types.

Peak serum levels of tobramycin in the range of 5 to 10 ug/mL are suggested for optimal therapeutic effectiveness. Persistently elevated peak concentrations (10 u/mL) have been shown to cause renal and eighth cranial nerve toxicity. Nephrotoxicity takes the form of damage to the proximal renal tubules, and is associated with impaired renal function. Central nervous system toxicity is most often manifested as damage to the vestibular and auditory branches of the eighth cranial nerve.

Trough levels offer a more discrete indication of impending toxicity since they more closely correspond to tissue levels and are less affected by sampling errors. Slowly rising trough levels have been shown to correspond to tissue accumulation of the drug, and levels greater than 2 ug/mL have been associated with renal failure in some patients.