Amikacin's niche is that it also has activity against more resistant gram-negative bacilli such as Acinetobacter baumanii and Pseudomonas aeruginosa. It also has excellent activity against most aerobic gram-negative bacilli from the Enterobacteriaceae family, including Nocardia and some Mycobacterium (M. avium-intracellulare, M. chelonae, and M. fortuitum). Unlike gentamicin, amikacin does not provide synergistic activity against Enterococcus faecium when combined with beta-lactam antibiotics.
Amikacin is rarely used alone and often combined with other antibiotics.
Amikacin binds irreversibly to the 30 S bacterial ribosome subunit, resulting in interference with a reading of the genetic code and inhibition of protein synthesis. Amikacin, as well as the rest of the aminoglycosides, are generally bacteriocidal and probably have an additional mechanism of action which is yet to be determined.
Amikacin can be administered parenterally or via nebulization. There is no oral formula of the drug available because the drug is not absorbed from the gastrointestinal tract. Amikacin can be administered intramuscularly when intravenous access is not available. In some patients with meningitis, it can be administered intrathecally and reaches high levels in the cerebrospinal fluid immediately.
Dosing based on weight (Kg):
> 50 mL/min (CrCL): no adjustment
30-50 mL/min: every 12 to 18 hrs
10-29 mL/min: every 18 to 24 hr
< 10 mL/min: dose based on levels or consult a pharmacist.
Once Daily Dosing:
Not to be used in patients with ascites, > 20% BSA burns, pregnant patients, or patients on dialysis. (Use conventional dosing or consult pharmacist.)
15 mg/kg per dose once daily
Adjustment for renal impairment:
60 mL/min (CrCL) and above: every 24 hours
40-59 mL/min: every 36 hours
30-39 mL/min: every 48 hours
< 30mL/min: Use conventional dosing method
Intravitreal: 0.4 mg/0.1 mL of Normal Saline (preservative free formulation, OFF LABEL)
Intrathecal/intraventricular: 5 to 50mg/day, usual dose is 30mg (preservative free formulation, OFF LABEL)
*IBW: Ideal body weight, ABW: Actual body weight, DBW: Dosing body weight, CrCL: Creatinine clearance (not GFR)
There is also liposomal amikacin undergoing clinical trials for the treatment of respiratory infections in patients with cystic fibrosis and bronchiectasis. In the trials, the liposomal formula is being used to treat nontuberculous bacteria and pseudomonas aeruginosa.
Amikacin has to be used with great caution in the elderly population who tend to have a marginal renal function. In addition, young children also do not have a fully developed renal system, and hence smaller doses should be used.
Major Adverse Effects
Nephrotoxicity is the most common, occurring in 1% to 10% of patients. The nephrotoxicity is reversible if detected early and the drug discontinued. Renal damage is more likely to occur in patients who are dehydrated, have a low glomerular filtration rate, have diabetes, sepsis, fever, or are on NSAIDs.
Ototoxicity, vestibular and auditory (4% to 6%), can occur when high doses are used. The patient may complain of loss of balance and hearing loss. This can be permanent if drug therapy is continued for prolonged periods. The ototoxicity is believed to be due to the generation of oxidative free radicals which damage the hair cells in the cochlea. Many hospitals now routinely monitor hearing before, during, and after therapy in infants.
Neuromuscular blockade is less common.
Increase in BUN/Cr (5% to 25%), drug fever, and Rash (less common).
Neurotoxicity may present in some patients with paresthesias, tingling, and numbness.
Patients may demonstrate hypersensitivity to amikacin, other aminoglycosides, or any component of the formulation.
Amikacin can pass through breast milk and the placenta. Hence it is not recommended in women who are pregnant as the drug may cause congenital deafness in the infant. Even though only small amounts pass into breast milk, experts do not recommend breastfeeding while on amikacin.
In general, amikacin is not used in infants. In addition, since infants and small children tend to have a large volume of distribution, the drug remains in the circulation for prolonged periods.
Amikacin should not be used in combination with other drugs that have the potential to cause renal and auditory toxicity. The list of medications that should be avoided include amphotericin B, acyclovir, capreomycin, bacitracin, vancomycin and cisplatin. In addition, amikacin should not be used in patients who are receiving neuromuscular blockers because it can prolong the muscle paralysis and weakness.
Monitor renal function (BUN/Cr every 1 to 2 days based on stability of renal function), Ins and Outs (daily), hearing parameters (baseline and weekly audiograms), symptoms of vertigo/dizziness (daily), peak levels (conventional dosing, no need in once-daily dosing) and trough levels (both conventional and once-daily dosing, repeat every 2 to 3 days and prolong if levels are stable.
Conventional Dosing Levels
Once Daily Dosing Levels:
No antidote for toxicity is available, only 20% dialyzable; however, this is variable based on hemodialysis filter.
Amikacin when combined with penicillins can have an additive effect on certain microorganisms.
Amikacin when combined with carbapenems can have a synergistic effect against some gram-positive organisms.
Clindamycin, chloramphenicol, and tetracycline have the ability to inactivate amikacin and other aminoglycosides.
High-ceiling diuretics like furosemide not only increase ototoxicity themselves but they also have the potential to increase the concentration of amikacin, thereby worsening the ototoxicity.
Other medications that can increase levels of amikacin in blood include NSAIDs (especially indomethacin) and quinidine.
Amikacin is a very useful drug to treat gram-negative infections. Healthcare workers including nurse practitioners who prescribe it should always check renal function regularly as the drug is nephrotoxic.