From the Guidelines
Tobramycin is generally preferred over amikacin due to its lower risk of nephrotoxicity and ototoxicity, as evidenced by studies showing amikacin may cause deafness and nephrotoxicity in a higher percentage of patients 1. When considering the use of tobramycin versus amikacin, several factors must be taken into account, including the severity of the infection, local resistance patterns, and patient-specific factors such as renal function.
- The typical adult dose for tobramycin is 3-5 mg/kg/day divided into every 8 hours, while amikacin is dosed at 15-20 mg/kg/day, usually given once daily.
- Both medications require therapeutic drug monitoring due to their narrow therapeutic index, with target peak levels for tobramycin of 5-10 mcg/mL and for amikacin 20-35 mcg/mL.
- Amikacin is often reserved as a second-line agent when other aminoglycosides might be ineffective due to resistance.
- The risk of ototoxicity, including high-frequency hearing loss, is higher with amikacin, occurring in 24% of patients receiving amikacin in one report 1.
- Nephrotoxicity is also a concern with amikacin, with renal impairment seen in 8.7% of patients receiving the drug, compared to a lower frequency in patients with no risk factors 1.
- Careful monitoring of kidney function, including serum creatinine, BUN, and drug levels, is essential during treatment with either medication, especially in elderly patients or those with pre-existing renal impairment.
From the FDA Drug Label
CLINICAL PHARMACOLOGY: Microbiology Mechanism of Action Amikacin, an aminoglycoside, binds to the prokaryotic ribosome, inhibiting protein synthesis in susceptible bacteria. Amikacin resists degradation by certain aminoglycoside inactivating enzymes known to affect gentamicin, tobramycin, and kanamycin. INDICATIONS AND USAGE Tobramycin for Injection, is an aminoglycoside antibacterial indicated for the treatment of serious bacterial infections caused by susceptible isolates of the designated bacteria in the diseases listed below
The main difference between Tobramycin and Amikacin is their spectrum of activity and resistance to certain enzymes.
- Amikacin is effective against bacteria that are resistant to Tobramycin due to its resistance to certain aminoglycoside inactivating enzymes.
- Both Amikacin 2 and Tobramycin 3 are used to treat serious bacterial infections, but their specific indications and susceptible bacteria may vary.
- Amikacin has a broader spectrum of activity against Gram-negative bacteria, including Pseudomonas species, Escherichia coli, and Klebsiella species.
- Tobramycin is also effective against these bacteria, but its use may be limited by resistance to certain enzymes.
From the Research
Comparison of Tobramycin and Amikacin
- Both tobramycin and amikacin are aminoglycoside antibiotics used to treat serious gram-negative bacterial infections 4, 5, 6, 7.
- Amikacin is active against most gram-negative bacteria, including gentamicin- and tobramycin-resistant strains, making it a preferred choice in cases of suspected resistance 4, 5, 6, 7.
- Tobramycin is effective against a wide range of Enterobacteriaceae and many Pseudomonas aeruginosa organisms, but its use may be limited in areas with high gentamicin resistance 5, 6.
- Amikacin achieves high and predictable serum concentrations, with a favorable therapeutic index, and is less inactivated by semisynthetic penicillins compared to other aminoglycosides 4, 6, 7.
- Both tobramycin and amikacin can cause nephrotoxicity and ototoxicity, but the potential for these adverse effects is not significantly different between the two antibiotics 4, 7.
- The use of amikacin is debatable in hospitals without substantial aminoglycoside resistance, as it has not been shown to have increased clinical efficacy compared to other aminoglycosides for infections caused by susceptible bacteria 7.
- Medication-induced nephrotoxicity, including that caused by aminoglycosides like tobramycin and amikacin, remains a common cause of acute kidney injury among hospitalized patients, and prevention and early recognition are crucial to mitigate this risk 8.