Gentamicin

Gentamicin is an aminoglycoside antibiotic widely used in Gram negative infections (i.e. Pseudomonas aeruginosa, Proteus mirabilis., Providencia stuartii, Escherichia coli, Klebsiella  Enterobacter, Serratia species, Citrobacter freundii, and Acinetobacter species). 

Gentamicin is typically given 2 to 3 times per day by intramuscular or intravascular injection. The therapeutic goal is to reach peak blood concentration between 3 and 12 ug/mL. Therapeutic drug monitoring is important to prevent development of ototoxicity and nephrotoxicity. Nephrotoxicity and ototoxicity may be more related to trough levels than to peak levels.

Variability in renal function, extracellular fluid volume, fever, anemia and concomitant administration with carbenicillin or lasix significantly affects individual levels. 

Gentamicin is measured by immunoassay. Specimen requirement is one plain red top tube of blood. The therapeutic trough level is 0-2 ug/mL. 

Reference

Gonzalez LS, Spencer JP: Aminoglycosides: a practical review. Am Fam Physician, 1998;5:58(8):1811-1820.