Amikacin is a member of the aminoglycoside family of antibiotics. By binding to the 30s ribosomal subunit of a prokaryotic organism, amikacin inhibits protein synthesis and is therefore bactericidal. It is highly active against most gram-negative bacteria,
Nocardia, and
Mycobacteria, and is often used to provide additional gram-negative coverage when infection is causing critical illness. Like other aminoglycosides, amikacin has a narrow therapeutic index and measuring timed serum levels of the drug is critical in administering it both efficaciously and safely.
Peak serum levels correspond to the bactericidal effect of the drug, since efficacy of aminoglycosides is dose-dependent. Amikacin, like other aminoglycosides, is most effective when the ratio of peak level to minimum inhibitory concentration (MIC) of the organism is 10 or greater. Serum samples for peak concentrations should be collected one hour after the start of IV infusion and 60-90 mins after IM injection; in people with critical illness, the peak serum levels should be collected after the first dose. Ensuring adequate peak serum level is necessary to avoid underdosing, particularly in people with large volumes of distribution. Note that peak levels of more than 35-40mcg/mL for prolonged periods of time correlate with nephrotoxicity incidence.
Ototoxicity and nephrotoxicity are two of the most concerning adverse effects of amikacin. Serum trough levels, which should be drawn 30 minutes before the next dose (or prior to the next scheduled session in people on HD), correspond to toxicity. For once daily dosing, trough levels should be <1mcg/mL; for multiple daily dose regimen, trough levels should be 1-4mcg/mL if the infection is less severe (e.g., no sepsis, no bacteremia) or 4-8mcg/mL in severe infection. Significant nephrotoxicity and ototoxicity have been associated with amikacin trough levels >10 mcg/mL.
References: Medscape Reference: Amikacin Level