Tobramycin is an aminoglycoside antibiotic used to treat severe infections caused by Gram negative bacteria that are resistant to other antibiotics. Susceptible bacteria include Pseudomonas, Enterobacter, Serratia, Proteus, Acinetobacter, and Klebsiella. Under aerobic conditions, tobramycin inhibits protein synthesis and is bactericidal.

Tobramycin can be administered intramuscularly or intravenously. Because fat stores are poorly accessible to tobramycin, dosage should be calculated based on lean body weight rather than actual body weight. Less than 10% of circulating drug is protein bound. Tobramycin is not metabolized. The kidney eliminates parent drug almost entirely. In patients with normal renal function, 60% of a dose is excreted in 6 hours and 90% within 24 hours.

Tobramycin has a narrow therapeutic to toxic ratio. Peak and trough levels should be measured beginning on the second or third day of treatment to assess dosage adequacy and to minimize the risk of ototoxicity and nephrotoxicity.Both levels should be repeated every 2?3 days if the patient is receiving more than 1.5 mg/kg for 10 days or more. Nephrotoxicity and ototoxicity may be more related to the height of the trough concentration or frequency of dose than peak serum concentration. Variability in renal function, extracellular fluid volume, fever, anemia and concomitant administration of carbenicillin or Lasix significantly affects individual levels.Trough levels should be drawn immediately before next dose. Peak levels should be drawn 30?60 minutes after and IV infusion ends or 60 minutes after an IM injection.

Therapeutic peak range is 3 to 10 ug/mL and the critical value is >12.0 ug/mL. Therapeutic trough range is 0 to 2 ug/mL and the critical value is >2.5 ug/mL.

Specimen requirement is one plain red top tube of blood.

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