Gentamicin Injection

Information from MWI Animal Health:

Gentamicin Sulfate Solution is recommended for the control of bacterial infections of the uterus (metritis) in horses and as an aid in improving conception in mares with uterine infections caused by bacteria sensitive to gentamicin. For intrauterine infusion. The recommended dose is 20 to 25 mL (2.0-2.5 grams) Gentamicin Sulfate Solution per day for 3 to 5 days during estrus. Each dose should be diluted with 200-500 mL of sterile physiological saline before aseptic uterine infusion. 

Information from Drugs.com, by Vet Tek:

Gentamicin Sulfate Solution Caution

Federal law restricts this drug to use by or on the order of a licensed veterinarian.

Description

Each mL of Gentamicin sulfate veterinary equivalent to 100 mg gentamicin base; 2.4 mg sodium metabisulfite; 0.8 mg sodium sulfite, anhydrous; 0.1 mg edetate disodium; 10 mg benzyl alcohol as preservative; water for injection q.s.

CHEMISTRY: Gentamicin is a mixture of aminoglycoside antibiotics derived from the fermentation of Micromonospora purpurea. Gentamicin sulfate is a mixture of sulfate salts of the antibiotics produced in this fermentation. The salts are weakly acidic, freely soluble in water, and stable in solution.

ANTIBACTERIAL ACTIVITY: In vitro antibacterial activity has shown that gentamicin is active against most gram-negative and gram-positive bacteria isolated from domestic animals.¹ Gentamicin is active against Pseudomonas aeruginosa, indole-positive and -negative Proteus species, Escherichia coli, Klebsiella species, Enterobacter species, Alcaligenes species, Staphylococcus species, and Streptococcus species.

Pharmacology

Studies in man indicate that recommended doses of gentamicin produce serum concentrations bactericidal for most bacteria sensitive to gentamicin within an hour after intramuscular injection; these concentrations last for 6 to 12 hours.² Some 30% of the administered dose of gentamicin is bound by serum proteins and released as the drug is excreted.

Gentamicin is excreted almost entirely by glomerular filtration. High concentrations of the active form are found in the urine. Fifty to 100% of the gentamicin injected can be recovered unchanged within 24 hours from the urine of patients with normal renal function. A small amount is excreted into the bile.

TOXICITY STUDIES: No toxic effects were observed in rats given gentamicin sulfate 20 mg/kg/day for 24 days; in cats given 10 mg/kg/day for 40 days. Gentamicin sulfate given to dogs at 6 mg/lb/day, 6 days weekly for 3 weeks, caused no detectable kidney damage. At higher doses, impairment of equilibrium and renal function were observed in these species.

Gentamicin Sulfate Solution Indications

Gentamicin Sulfate Solution is recommended for the control of bacterial infections of the uterus (metritis) in horses and as an aid in improving conception in mares with uterine infections caused by bacteria sensitive to gentamicin.

Bacteriologic studies should be conducted to identify the causative organism and to determine its sensitivity to gentamicin sulfate. Sensitivity discs of the drug are available for this purpose.

Dosage and Administration

The recommended dose is 20 to 25 mL (2.0 - 2.5 grams) gentamicin sulfate solution per day for 3 to 5 days during estrus. Each dose should be diluted with 200-500 mL of sterile physiological saline before aseptic uterine infusion.

Contraindications

There are no known contraindications to this drug when used as directed.

PRECAUTION: If hypersensitivity to any of the components develops, or if overgrowth of nonsusceptible bacteria, fungi, or yeasts occurs, treatment with Gentamicin Sulfate Solution should be discontinued and appropriate therapy instituted.

Although Gentamicin Sulfate Solution is not spermicidal, treatment should not be given the day of breeding.

Warning

Do not use for horses intended for human consumption.

Side Effects

There have been no reports of drug hypersensitivity or adverse side effects following the recommended intrauterine infusion of gentamicin sulfate solution combined with sterile physiological saline in mares.

Information from Plumb's Veterinary Drug Handbook, 7th Edition, by Donald C. Plumb:

Aminoglycosides are contraindicated in patients who are hypersensitive to them. Because these drugs are often the only effective agents in severe gram-negative infections, there are no other absolute contraindications to their use. However, they should be used with extreme caution in patients with pre-existing renal disease with concomitant monitoring and dosage interval adjustments made. Other risk factors for the development of toxicity include age (both neonatal and geriatric patients), fever, sepsis, and dehydration.

Because aminoglycosides can cause irreversible ototoxicity, they should be used with caution in working dogs (e.g. seeing-eye, herding, dogs for the hearing impaired, etc). Aminoglycosides should be used with caution in patients with neuromuscular disorders (e.g. myasthenia gravis) due to their neuromuscular blocking activity. They should not be used in animals with botulism. Sighthouns dogs may require reduced dosages or aminoglycosides, as they have significantly smaller volumes of distribution. Because aminoglycosides are eliminated primarily through renal mechanisms, they should be used cautiously, preferably with serum monitoring and dosage adjustment in neonatal or geriatric animals. Aminoglycosides are often considered contraindicated in rabbits as they adversely effect the GI flora balance in these animals. Use with Caution. 

The aminoglycosides are infamous for their nephrotoxic and ototoxic effects. The nephrotoxic (tubular necrosis) mechanisms of these drugs are not completely understood. Nephrotoxicity is usually reversible once the drug is discontinued, While gentamicin may be more nephrotoxic that the other aminoglycosides, the incidences of nephrotoxicity with all these agents require equal caution and monitoring. Ototoxicity (8th cranial nerve toxicity) of the aminoglycosides can manifest by either auditory and/or vestibular clinical signs, and may be irreversible. Vestibular clinical signs are more frequent with streptomycin, gentamicin, or tobramycin. Auditory clinical signs are more frequent with amikacin, neomycin, or kanamycin, but other forms can appear with any of the drugs. Cats are apparently very sensitive to the vestibular effects of the aminoglycosides. The aminoglycosides can also cause neuromuscular blockade, facial edema, pain/inflammation at injection site, peripheral neuropathy, and hypersensitivity reactions. Rarely, GI clinical signs, hematologic, and hepatic effects have been reported.

Aminoglycosides can cross the placenta and, while rare, may cause 8th cranial nerve toxicity or nephrotoxicity in fetuses. Because the drug should only be used in serious infections, the benefits of therapy may exceed the potential risks. While small amounts of gentamicin may be excreted into milk, the risk to nursing offspring appears minimal.

Should an inadvertent overdose by administered, three treatments have been recommended. Hemodialysis is very effective in reducing serum levels of the drug, but is not a viable option for most veterinary patients. Peritoneal dialysis will also reduce serum levels, but is much less effective. Complexation of drug with ticarcillin is reportedly nearly as effective as hemodialysis. 

The following drugs may interact with gentamicin: beta lactam antibiotics, cephalosporins, loop or osmotic diuretics, other nephrotoxic drugs, neuromuscular blocking agents, general anesthetics.