Amikacin, Trough

Serum or plasma

1 mL

0.3 mL

Red-top tube or green-top (heparin) tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.

Amikacin is used to treat serious infections caused by susceptible aerobic gram-negative bacilli (e.g., a number of the Enterobacteriaceae, P. aeruginosa). Such infections include bacteremias; intra-abdominal, soft tissue (including burns), bone or joint, lower respiratory tract and complicated urinary tract infections, and meningitis.

The major advantage of amikacin is its superior resistance profile. Thus, it is the aminoglycoside of choice for infections caused by aerobic gram-negative bacilli that are known or suspected to be resistant to other aminoglycosides. It should be the aminoglycoside of choice for general use in hospitals where the prevalence of resistance to gentamicin and tobramycin is known to be high or when there is concern about gentamicin- and tobramycin-resistant gram-negative bacilli in a particular clinical situation.

Because amikacin is the only currently available aminoglycoside effective against many gentamicin- and tobramycin-resistant organisms, many infectious disease experts have felt that its use should be restricted to minimize the emergence of additional resistant strains. However, there is no evidence that such restriction has delayed the emergence of resistance. Furthermore, reports from hospitals that rely on amikacin as the primary aminoglycoside suggest that resistance to amikacin does not increase despite widespread use and gentamicin/tobramycin resistance actually may decrease. Nevertheless, general use of amikacin in hospitals without a gentamicin or tobramycin resistance problem remains controversial. Amikacin is considerably more expensive than gentamicin, an important consideration in a cost-conscious environment.

Immunoassay (IA)

Therapeutic: peak: 20.0–30.0 µg/mL, trough: 1.0–8.0 µg/mL

Amikacin is cleared by the kidney and accumulates in renal tubular cells. Nephrotoxicity is most closely related to the length of time that trough levels are >8 μg/mL. Creatinine levels should be monitored every two to three days as an indicator of impending renal toxicity. The initial toxic result is nonoliguric renal failure that is usually reversible if the drug is discontinued. Continued administration of amikacin may produce oliguric renal failure. Nephrotoxicity may occur in as many as 10% to 25% of patients receiving aminoglycosides; most of this toxicity can be avoided by monitoring levels and adjusting dosing schedules accordingly.

Aminoglycosides may also cause irreversible ototoxicity that manifests itself clinically as hearing loss. Aminoglycoside ototoxicity is relatively uncommon and clinical trials in which levels were carefully monitored and dosing adjusted failed to show a correlation between auditory toxicity and plasma aminoglycoside levels. In situations in which dosing is not adjusted, however, sustained high levels may be associated with ototoxicity. This association is far from clear-cut, and new once-daily dosing regimens (and associated high peak serum concentrations) that fail to enhance toxicity further complicate this issue.