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Gentamicin Sulfate Injection, USP is a sterile, nonpyrogenic solution of gentamicin sulfate in water for injection. It is administered by the intramuscular or intravenous route.
Each milliliter (mL) contains gentamicin sulfate equivalent to 40 mg gentamicin base with sodium metabisulfite 2.9 mg and edetate disodium anhydrous 0.1 mg added as stabilizer, methylparaben 1.8 mg and propylparaben 0.2 mg added as preservatives. Headspace nitrogen gassed. May contain sulfuric acid and/or sodium hydroxide for pH adjustment. The pH is 3.8 (3.0 to 5.5).
Gentamicin is classified as an aminoglycoside antibiotic and is derived from Micromonospora purpurea, an actinomycete.
The chemical name for gentamicin C1A is: 0-3-Deoxy-4-C-methyl-3-(methylamino)-β-L-arabinopyranosyl-(1→6)-0-[2,6-diamino-2,3,4,6-tetradeoxy-α-D-erythro-hexopyranosyl-(1→4)]-2-deoxy-D-streptamine.
Gentamicin Sulfate, USP is chemically designated gentamicin sulfate, a white to buff powder soluble in water. It has the following structural formula:
Since gentamicin is distributed in extracellular fluid, peak serum concentrations may be lower than usual in adult patients who have a large volume of this fluid. Serum concentrations of gentamicin in febrile patients may be lower than those in afebrile patients given the same dose. When body temperature returns to normal, serum concentrations of the drug may rise. Febrile and anemic states may be associated with a shorter than usual serum half-life. (Dosage adjustment is usually not necessary.) In severely burned patients, the half-life may be significantly decreased and resulting serum concentrations may be lower than anticipated from the mg/kg dose.
Protein binding studies have indicated that the degree of gentamicin binding is low, depending upon the methods used for testing, this may be between 0 and 30%.
After initial administration to patients with normal renal function, generally 70% or more of the gentamicin dose is recoverable in the urine in 24 hours; concentrations in urine above 100 mcg/mL may be achieved. Little, if any metabolic transformation occurs; the drug is excreted principally by glomerular filtration. After several days of treatment, the amount of gentamicin excreted in the urine approaches the daily dose administered. As with other aminoglycosides, a small amount of the gentamicin dose may be retained in the tissues, especially in the kidneys. Minute quantities of aminoglycosides have been detected in the urine weeks after drug administration was discontinued. Renal clearance of gentamicin is similar to that of endogenous creatinine.
In patients with marked impairment of renal function, there is a decrease in the concentration of aminoglycosides in urine and in their penetration into defective renal parenchyma. This decreased drug excretion, together with the potential nephrotoxicity of aminoglycosides, should be considered when treating such patients who have urinary tract infections.
Probenecid does not affect renal tubular transport of gentamicin.
