Amikacin for Veterinary Use

Therapeutic Class: Aminoglycoside antibiotic

Species: Dogs, Cats, Horses

May Be Prescribed For: Susceptible Bacterial Infections

Amikacin is an aminoglycoside antibiotic that is used to treat serious gram-negative bacterial infections. Other antibiotics in this family include gentamicin, streptomycin, neomycin, kanamycin, and tobramycin. Amikacin and gentamicin are the most commonly used in veterinary medicine. The aminoglycoside antibiotics are bactericidal and are particularly effective against aerobic gram-negative bacteria including E. Coli, Proteus, Pseudomonas, Salmonella, Shigella, Serratia, and Enterobacter. There are some gram-positive Staphyloccus that are sensitive to amikacin although generally the aminoglycosides are combined with other antibiotics when both gram-negative and gram-positive bacteria are present. Amikacin has no activity against fungi, or most anaerobic bacteria. Aminoglycosides also have poor activity in the presence of pus or organic debris. Amikacin has a broader spectrum of activity than some of the other members of this group and is often used for bacterial infections resistant to gentamicin.

The mechanism of action for amikacin is through disruption of the bacterial cell wall, irreversible binding of the 30S ribosomal subunit, and inhibition of bacterial protein synthesis. The bactericidal properties of amikacin are concentration dependent and there is significant bactericidal activity even after drug concentrations are below the minimum inhibitory concentration (MIC). Amikacin and other aminoglycosides are eliminated via the kidney and can be nephrotoxic. Animals with decreased kidney function may have a significantly increased half-life.

Aminoglycosides are poorly absorbed from the gastrointestinal (GI) tract and must be given parenterally. Amikacin is also used in topical preparations for the skin, ears and eyes.

Systemic amikacin is used to treat serious gram-negative infections. It is usually given once a day, because it is a concentration dependant antibiotic. Amikacin may be combined with other antibiotics to provide coverage for gram positive bacteria. It is less nephrotoxic than gentamicin although all aminoglycosides have the potential for both renal and otic toxicity. There are a number of factors that increase the risk of nephrotoxicity: see precautions.

Amikacin is frequently used in topical otic-preparations to treat susceptible bacterial infections (most commonly Pseudomonas Aeruginosa). Aminoglycoside antibiotics have poor activity in the presence of pus and cellular debris. Proper cleaning of the ear will increase the effectiveness of topical treatments with amikacin.

Amikacin and other aminoglycosides are commonly used in ophthalmic preparations to treat corneal ulcers. Pseudomonas aeruginosa is the most-common gram-negative bacteria found from ocular cultures. Frequent ophthalmic application appears to be an important factor for treatment success.

Systemic amikacin is used to treat serious gram-negative infections in adult horses and foals. It is frequently used with intravenous penicillins to provide additional gram-positive coverage. Amikacin is generally preferred over gentamicin for systemic use in neonatal foals. The dosing interval in foals can be variable and frequently is much longer than that in adult horses. If renal function or hydration status is questionable, other antibiotics outside the aminoglycoside family may be preferable. Amikacin is also used for ophthalmic preparations, regional limb perfusion, joint lavage, and intra-articular injections.

• Systemic use of amikacin and other aminoglycoside antibiotics are usually reserved for serious illnesses because of the risk of nephrotoxicity and ototoxicity.
• When using amikacin or other aminoglycoside antibiotics, monitoring of renal function and peak trough drug concentrations can be very useful to decrease the risks of nephrotoxicity. Nephrotoxicity may be reversible once drug is discontinued.
• Ototoxicity may present as hearing loss or vestibular signs and may be irreversible. Cats are more sensitive to vestibular damage due to aminoglycosides.
• Injection site reactions may accur with intramuscular injection.
• Other less common side effects include neuromuscular blockade, facial edema, and peripheral neuropathy.
• Gastrointestinal side effects are rare.

• Prolonged treatment, electrolyte abnormalities (hyponatremia, hypokalemia), acidosis, and the use with other potentially nephrotoxic drugs increases risk of nephrotoxicity.
• Amikacin crosses the placenta and has been reported to cause both nephrotoxicity and ototoxicity in fetuses. It should only be used during pregnancy when the benefits exceed the potential risks. Amikacin is also found in maternal milk, although neonatal diarrhea is possible, it is not generally an issue.

• Amikacin should be avoided or used with caution with other drugs that have potential toxicity to the ear, kidneys, or nervous system.
• Diuretics such as furosemide increase the risk associated with renal toxicity from aminoglycoside antibiotics. Other potential nephrotoxic drugs include: Cisplatin, amphotericin B, polymyxin B, and vancomycin.
• Phenylbutazone has been shown to increase the elimination half-life of gentamicin. This work has not been repeated with amikacin.
• General anesthestics, and neuromuscular blocking agents may increase the risk of neuromuscular blockade.

Plumb's Veterinary Drug Handbook mentions three possible treatments for systemic overdose: hemodialysis, peritoneal dialysis, and complexation using of the penicillins. Articles in the human literature refer to the use of hemodialysis and the importance of aggressive diuresis with intravenous fluids.