glomerular filtration. The half-life of tobramycin in serum or plasma correlates closely with renal function and thus is quite variable between individuals and within one individual over time. Serum or plasma tobramycin concentration is also impacted by mode of administration, the volume of extracellular fluid, the duration of the treatment and physiological changes during the illness and therapy.

Test Indications: The therapeutic range of tobramycin should be measured at peak as well as trough concentrations. In patients with pre-existing renal damage or those to whom tobramycin has been administered for prolonged periods or in doses above the therapeutic range, hearing impairment and/or nephrotoxicity may develop. Therefore, monitoring of peak and trough tobramycin serum or plasma levels is critical in the prevention of these serious complications with the adjustment of dosage administration as indicated.

Patient preparation instructions: Trough sample should be collected 45 minutes prior to the next dose. Peak sample should be collected 20 – 40 minutes post tobramycin infusion. Amikacin cross-reacts with this assay. Kanamycin cross-reacts significantly; however, the assay has not been optimized to quantitate this aminoglycoside. Aminoglycosides are not generally coadministered in clinical practice, although more than one aminoglycoside may be present when switching from treatment with one to another. Samples that contain tobramycin in combination with either amikacin or kanamycin cannot be

reliably quantitated by this assay

(mg/L = μg/mL)