Amikacin is a semisynthetic derivative of kanamycin; it is less toxic than the parent molecule (Figure 45–2). It is resistant to many enzymes that inactivate gentamicin and tobramycin, and it there-fore can be used against some microorganisms resistant to the latter drugs. Many gram-negative bacteria, including many strains of Proteus, Pseudomonas, Enterobacter, and Serratia, are inhibited by 1–20 mcg/mL amikacin in vitro. After injection of 500 mg of amikacin every 12 hours (15 mg/kg/d) intramuscularly, peak levels in serum are 10–30 mcg/mL.Strains of multidrug-resistant Mycobacterium tuberculosis, including streptomycin-resistant strains, are usually susceptible to amikacin. Kanamycin-resistant strains may be cross-resistant to amikacin. The dosage of amikacin for tuberculosis is 7.5–15 mg/ kg/d as a once-daily or two to three times weekly injection and always in combination with other drugs to which the isolate is susceptible.
Like all aminoglycosides, amikacin is nephrotoxic and ototoxic (particularly for the auditory portion of the eighth nerve). Serum concentrations should be monitored. Target peak serum concen-trations for an every-12-hours dosing regimen are 20–40 mcg/mL, and troughs should be maintained between 4 and 8 mcg/mL.