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Gentamicin Pediatric

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Gentamicin Pediatric

CLINICAL PHARMACOLOGY

After intramuscular administration of gentamicin (gentamicin injection pediatric) sulfate, peak serum concentrations usually occur between 30 and 60 minutes and serum levels are measurable for 6 to 8 hours. In infants, a single dose of 2.5 mg/kg usually provides a peak serum level in the range of 3 to 5 mcg/mL.When gentamicin (gentamicin injection pediatric) is administered by intravenous infusion over a two-hour period, the serum concentrations are similar to those obtained by intramuscular administration. Age markedly affects the peak concentrations: in one report, a 1 mg/kg dose produced mean peak concentrations of 1.58, 2.03, and 2.81 mcg/mL in patients six months to five years old, 5to 10 years old, and over10 years old, respectively.

In infants one week to six months of age, the half-life is 3 to 3½ hours. In full-term and large premature infants less than one week old, the approximate serum half-life of gentamicin (gentamicin injection pediatric) is 5½ hours. In small premature infants, the half-life is inversely related to birth weight. In premature infants weighing less than 1500 grams, the half-life is 11½ hours; in those weighing 1500 to 2000 grams, the half-life is eight hours; in those weighing over 2000grams, the half-life is approximately five hours.While some variation is to be expected due to a number of variables such as age, body temperature, surface area and physiologic differences, the individual patient given the same dose tends to have similar levels in repeated determinations.

Gentamicin (gentamicin injection pediatric) , like all aminoglycosides, may accumulate in the serum and tissues of patients treated with higher doses and/or for prolonged periods, particularly in the presence of impaired or immature renal function. In patients with immature or impaired renal function, gentamicin (gentamicin injection pediatric) is cleared from the body more slowly than in patients with normal renal function.The more severe the impairment, the slower the clearance. (Dosage must be adjusted.)

Since gentamicin (gentamicin injection pediatric) is distributed in extracellular fluid, peak serum concentrations may be lower than usual in patients who have a large volume of this fluid. Serum concentrations of gentamicin (gentamicin injection pediatric) 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 resultingserumconcentrationsmaybelowerthan anticipated from the mg/kg dose.

Protein-binding studies have indicated that the degree of gentamicin (gentamicin injection pediatric) binding is low, depending upon the methods used for testing, this may be between 0 and 30%.

In neonates less than three days old, approximately 10% of the administered dose is excreted in 12 hours; in infants 5 to 40 days old, approximately 40% is excreted over the same period. Excretion of gentamicin (gentamicin injection pediatric) correlates with postnatal age and creatinine clearance. Thus, with increasing postnatal age and concomitant increase in renal maturity, gentamicin (gentamicin injection pediatric) is excreted more rapidly. Little, ifany, metabolic transformation occurs; the drug is excreted principally by glomerular filtration. After several days of treatment, the amount of gentamicin (gentamicin injection pediatric) excreted in the urine approaches, but does not equal, the daily dose administered. As with other aminoglycosides, a small amount of the gentamicin (gentamicin injection pediatric) dose may be retained in the tissues, especially in the kidneys. Minute quantities of aminoglycosides have been detected in the urine of some patients weeks after drug administration was discontinued. Renal clearance of gentamicin (gentamicin injection pediatric) 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 (gentamicin injection pediatric) .

The endogenous creatinine clearance rate and the serum creatinine level have a high correlation with the half-life of gentamicin (gentamicin injection pediatric) in serum. Results of these tests may serve as guides for adjusting dosage in patients with renalim pairment (see DOSAGE AND ADMINISTRATION).

Following parenteral administration, gentamicin (gentamicin injection pediatric) can be detected in serum, lymph, tissues, sputum, andinpleural, synovial, and peritoneal fluids. Concentrations in renal cortex sometimes may be eight times higher than the usual serum levels. Concentrations in bile, in general, have been low and have suggested minimal biliary excretion. Gentamicin (gentamicin injection pediatric) crosses the peritoneal as well as the placental membranes.Since aminoglycosides diffuse poorly into the subarachnoid space after parenteral administration, concentrations of gentamicin (gentamicin injection pediatric) in cerebrospinal fluid are often low and dependent upon dose, rate of penetration, and degree of meningeal inflammation.There is minimal penetration of gentamicin (gentamicin injection pediatric) into ocular tissues following intramuscular or intravenous administration.

Microbiology

In vitro tests have demonstrated that gentamicin (gentamicin injection pediatric) is a bactericidal antibiotic which acts by inhibiting normal protein synthesis in susceptible microorganisms. It is active against a wide variety of pathogenic bacteria including Escherichia coli, Proteus species, (indole-positive and indole-negative), Pseudomonas aeruginosa, species of the Klebsiella-Enterobacter-Serratia group, Citrobacter species and Staphylococcus species (including penicillin-and methicillin-resistant strains). Gentamicin (gentamicin injection pediatric) is also active in vitro against species of Salmonella and Shigella. The following bacteria are usually resistant to aminoglycosides: Streptococcus pneumoniae, most species of streptococci, particularly group D and anaerobic organisms, such as Bacteroides species or Clostridium species.

In vitro studies have shown that an aminoglycoside combined with an antibiotic that interferes with cell wall synthesis may act synergistically against some group D streptococcal strains. The combination of gentamicin (gentamicin injection pediatric) and penicillin G has a synergistic bactericidal effect against virtually all strains of Streptococcus faecalis and its varieties (S. faecalis var. liquifaciens, S. faecalis var. zymogenes), S. faecium and S. durans. An enhanced killing effect against many of these strains has also been shown in vitro with combinations of gentamicin (gentamicin injection pediatric) and ampicillin, carbenicillin, nafcillin, or oxacillin.

The combined effect of gentamicin (gentamicin injection pediatric) and carbenicillin is synergistic for many strains of Pseudomonas aeruginosa. In vitro synergism against other gram-negative organisms has been shown with combinations of gentamicin (gentamicin injection pediatric) and cephalosporins. Gentamicin (gentamicin injection pediatric) may be active against clinical isolates of bacteria resistant to other aminoglycosides. Bacteria resistant to one aminoglycoside may be resistant to one or more other aminoglycosides. Bacterial resistance to gentamicin (gentamicin injection pediatric) is generally developed slowly.

Susceptibility Testing

If the disc method of susceptibility testing used is that described by Bauer et al. (Am J Clin Path 45:493, 1966; Federal Register 37:20525-20529, 1972), a disc containing 10 mcg of gentamicin (gentamicin injection pediatric) should give a zone of inhibition of 15 mm or more to indicate susceptibility of the infecting organism. Zones of 12 mm or less indicate that the infecting organism is likely to be resistant. Zones of greater than 12 mm and less than 15 mm indicate intermediate susceptibility. In certain conditions it may be desirable to do additional susceptibility testing by the tube or agar dilution method; gentamicin (gentamicin injection pediatric) substance is available for this purpose.

Last reviewed on RxList: 6/24/2008
This monograph has been modified to include the generic and brand name in many instances.

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