Garamycin Injectable (Schering)

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DESCRIPTION

Gentamicin sulfate, USP, a water-soluble antibiotic of the aminoglycoside group, is derived from Micromonospora purpurea , an actinomycete. GARAMYCIN Injectable is a sterile, aqueous solution for parenteral administration. Each mL contains gentamicin sulfate, USP equivalent to 40 mg gentamicin base; 1.8 mg methylparaben and 0.2 mg propylparaben as preservatives; 3.2 mg sodium bisulfite; and 0.1 mg edetate disodium.

CLINICAL PHARMACOLOGY

After intramuscular administration of GARAMYCIN Injectable, peak serum concentrations usually occur between 30 and 60 minutes and serum levels are measurable for 6 to 8 hours. When gentamicin is administered by intravenous infusion over a 2-hour period, the serum concentrations are similar to those obtained by intramuscular administration.

In patients with normal renal function, peak serum concentrations of gentamicin (mcg/mL) are usually up to four times the single intramuscular dose (mg/kg); for example, a 1.0 mg/kg injection in adults may be expected to result in a peak serum concentration up to 4 mcg/mL; a 1.5 mg/kg dose may produce levels up to 6 mcg/mL. 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 administered at 1.0 mg/kg every 8 hours for the usual 7- to 10-day treatment period to patients with normal renal function does not accumulate in the serum.

Gentamicin, 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 renal function. In adult patients, treatment with gentamicin dosages of 4 mg/kg/day or higher for 7 to 10 days may result in a slight, progressive rise in both peak and trough concentrations. In patients with impaired renal function, gentamicin 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 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.

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

Following parenteral administration, gentamicin can be detected in serum, lymph, tissues, sputum, and in pleural, 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 crosses the peritoneal as well as the placental membranes. Since aminoglycosides diffuse poorly into the subarachnoid space after parenteral administration, concentrations of gentamicin in cerebrospinal fluid are often low and dependent upon dose, rate of penetration, and degree of meningeal inflammation. There is minimal penetration of gentamicin into ocular tissues following intramuscular or intravenous administration.

Microbiology:    In vitro tests have demonstrated that gentamicin 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 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 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 and ampicillin, carbenicillin, nafcillin, or oxacillin.

The combined effect of gentamicin 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 and cephalosporins.

Gentamicin 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 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 should give a zone of inhibition of 15 mm or more to indicate susceptibility of the infecting organism. A zone of 12 mm or less indicates that the infecting organism is likely to be resistant. Zones 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 substance is available for this purpose.

INDICATIONS AND USAGE

GARAMYCIN Injectable is indicated in the treatment of serious infections caused by susceptible strains of the following microorganisms: Pseudomonas aeruginosa, Proteus species (indole-positive and indole-negative), Escherichia coli, Klebsiella-Enterobacter-Serratia species, Citrobacter species, and Staphylococcus species (coagulase-positive and coagulase-negative).

Clinical studies have shown GARAMYCIN Injectable to be effective in bacterial neonatal sepsis; bacterial septicemia; and serious bacterial infections of the central nervous system (meningitis), urinary tract, respiratory tract, gastrointestinal tract (including peritonitis), skin, bone, and soft tissue (including burns). Aminoglycosides, including gentamicin, are not indicated in uncomplicated initial episodes of urinary tract infections unless the causative organisms are susceptible to these antibiotics and are not susceptible to antibiotics having less potential for toxicity.

Specimens for bacterial culture should be obtained to isolate and identify causative organisms and to determine their susceptibility to gentamicin.

GARAMYCIN Injectable may be considered as initial therapy in suspected or confirmed gram-negative infections, and therapy may be instituted before obtaining results of susceptibility testing. The decision to continue therapy with this drug should be based on the results of susceptibility tests, the severity of the infection, and the important additional concepts contained in the " WARNINGS " Box. If the causative organisms are resistant to gentamicin, other appropriate therapy should be instituted.

In serious infections when the causative organisms are unknown, GARAMYCIN Injectable may be administered as initial therapy in conjunction with a penicillin-type or cephalosporin-type drug before obtaining results of susceptibility testing. If anaerobic organisms are suspected as etiologic agents, consideration should be given to using other suitable antimicrobial therapy in conjunction with gentamicin. Following identification of the organism and its susceptibility, appropriate antibiotic therapy should then be continued.

GARAMYCIN Injectable has been used effectively in combination with carbenicillin for the treatment of life-threatening infections caused by Pseudomonas aeruginosa . It has also been found effective when used in conjunction with a penicillin-type drug for the treatment of endocarditis caused by group D streptococci.

GARAMYCIN Injectable has also been shown to be effective in the treatment of serious staphylococcal infections. While not the antibiotic of first choice, GARAMYCIN Injectable may be considered when penicillins or other less potentially toxic drugs are contraindicated and bacterial susceptibility tests and clinical judgment indicate its use. It may also be considered in mixed infections caused by susceptible strains of staphylococci and gram-negative organisms.

In the neonate with suspected bacterial sepsis or staphylococcal pneumonia, a penicillin-type drug is also usually indicated as concomitant therapy with gentamicin.

CONTRAINDICATIONS

Hypersensitivity to gentamicin is a contraindication to its use. A history of hypersensitivity or serious toxic reactions to other aminoglycosides may contraindicate use of gentamicin because of the known cross-sensitivity of patients to drugs in this class.

WARNINGS

  (See boxed WARNINGS .)

Aminoglycosides can cause fetal harm when administered to a pregnant woman. Aminoglycoside antibiotics cross the placenta, and there have been several reports of total irreversible bilateral congenital deafness in children whose mothers received aminoglycosides including gentamicin during pregnancy. Animal reproduction studies conducted on rats and rabbits did not reveal evidence of impaired fertility or harm to the fetus due to gentamicin sulfate.

If gentamicin is used during pregnancy or if the patient becomes pregnant while taking gentamicin, she should be apprised of the potential hazard to the fetus.

GARAMYCIN Injectable contains sodium bisulfite, a sulfite that may cause allergic-type reactions including anaphylactic symptoms and life-threatening or less severe asthmatic episodes in certain susceptible people. The overall prevalence of sulfite sensitivity in the general population is unknown and probably low. Sulfite sensitivity is seen more frequently in asthmatic than in nonasthmatic people.

PRECAUTIONS

Neurotoxic and nephrotoxic antibiotics may be absorbed in significant quantities from body surfaces after local irrigation or application. The potential toxic effect of antibiotics administered in this fashion should be considered.

Increased nephrotoxicity has been reported following concomitant administration of aminoglycoside antibiotics and cephalosporins.

Neuromuscular blockade and respiratory paralysis have been reported in the cat receiving high doses (40 mg/kg) of gentamicin. The possibility of these phenomena occurring in man should be considered if aminoglycosides are administered by any route to patients receiving anesthetics, or to patients receiving neuromuscular blocking agents, such as succinylcholine, tubocurarine, or decamethonium, or in patients receiving massive transfusions of citrate-anticoagulated blood. If neuromuscular blockade occurs, calcium salts may reverse it.

Aminoglycosides should be used with caution in patients with neuromuscular disorders, such as myasthenia gravis, since these drugs may aggravate muscle weakness because of their potential curare-like effects on the neuromuscular junction. During or following gentamicin therapy, paresthesias, tetany, positive Chvostek and Trousseau signs, and mental confusion have been described in patients with hypomagnesemia, hypocalcemia, and hypokalemia. When this has occurred in infants, tetany and muscle weakness has been described. Both adults and infants required appropriate corrective electrolyte therapy.

Elderly patients may have reduced renal function which may not be evident in the results of routine screening tests, such as BUN or serum creatinine. A creatinine clearance determination may be more useful. Monitoring of renal function during treatment with gentamicin, as with other aminoglycosides, is particularly important in such patients. A Fanconi-like syndrome, with aminoaciduria and metabolic acidosis, has been reported in some adults and infants being given gentamicin injections.

Cross-allergenicity among aminoglycosides has been demonstrated.

Patients should be well hydrated during treatment.

Although the in vitro mixing of gentamicin and carbenicillin results in a rapid and significant inactivation of gentamicin, this interaction has not been demonstrated in patients with normal renal function who received both drugs by different routes of administration. A reduction in gentamicin serum half-life has been reported in patients with severe renal impairment receiving carbenicillin concomitantly with gentamicin.

Treatment with gentamicin may result in overgrowth of nonsusceptible organisms. If this occurs, appropriate therapy is indicated.

See " WARNINGS " Box regarding concurrent use of potent diuretics and regarding concurrent and/or sequential use of other neurotoxic and/or nephrotoxic antibiotics and for other essential information.

Nursing Mothers -- Because of the potential for serious adverse reactions from aminoglycosides in nursing infants, a decision should be made to discontinue nursing or therapy taking into account the importance of the drug to the mother.

ADVERSE REACTIONS

Nephrotoxicity    Adverse renal effects, as demonstrated by the presence of casts, cells, or protein in the urine or by rising BUN, NPN, serum creatinine, or oliguria, have been reported. They occur more frequently in patients with a history of renal impairment and in patients treated for longer periods or with larger dosage than recommended.

Neurotoxicity    Serious adverse effects on both vestibular and auditory branches of the eighth cranial nerve have been reported, primarily in patients with renal impairment (especially if dialysis is required) and in patients on high doses and/or prolonged therapy. Symptoms include dizziness, vertigo, ataxia, tinnitus, roaring in the ears, and hearing loss, which, as with the other aminoglycosides, may be irreversible. Hearing loss is usually manifested initially by diminution of high-tone acuity. Other factors which may increase the risk of toxicity include excessive dosage, dehydration, and previous exposure to other ototoxic drugs.

Peripheral neuropathy or encephalopathy, including numbness, skin tingling, muscle twitching, convulsions, and a myasthenia gravis-like syndrome, have been reported.

Note:    The risk of toxic reactions is low in patients with normal renal function who do not receive GARAMYCIN Injectable at higher doses or for longer periods of time than recommended.

Other reported adverse reactions possibly related to gentamicin include: respiratory depression, lethargy, confusion, depression, visual disturbances, decreased appetite, weight loss, and hypotension and hypertension; rash, itching, urticaria, generalized burning, laryngeal edema, anaphylactoid reactions, fever, and headache; nausea, vomiting, increased salivation, and stomatitis; purpura, pseudotumor cerebri, acute organic brain syndrome, pulmonary fibrosis, alopecia, joint pain, transient hepatomegaly, and splenomegaly.

Laboratory abnormalities possibly related to gentamicin include: increased levels of serum transaminase (SGOT, SGPT), serum LDH, and bilirubin; decreased serum calcium, magnesium, sodium, and potassium; anemia, leukopenia, granulocytopenia, transient agranulocytosis, eosinophilia, increased and decreased reticulocyte counts, and thrombocytopenia. While clinical laboratory test abnormalities may be isolated findings, they may also be associated with clinically related signs and symptoms. For example, tetany and muscle weakness may be associated with hypomagnesemia, hypocalcemia, and hypokalemia.

While local tolerance of GARAMYCIN Injectable is generally excellent, there has been an occasional report of pain at the injection site. Subcutaneous atrophy or fat necrosis suggesting local irritation has been reported rarely.

OVERDOSAGE

In the event of overdose or toxic reactions, hemodialysis may aid in the removal of gentamicin from the blood, and is especially important if renal function is, or becomes, compromised. The rate of removal of gentamicin is considerably less by peritoneal dialysis than it is by hemodialysis.

DOSAGE AND ADMINISTRATION

GARAMYCIN Injectable may be given intramuscularly or intravenously. The patient's pretreatment body weight should be obtained for calculation of correct dosage. The dosage of aminoglycosides in obese patients should be based on an estimate of the lean body mass. It is desirable to limit the duration of treatment with aminoglycosides to short term.

DOSAGE FOR PATIENTS WITH NORMAL RENAL FUNCTION

Adults:    The recommended dosage of GARAMYCIN Injectable for patients with serious infections and normal renal function is 3 mg/kg/day, administered in three equal doses every 8 hours (TABLE I).

For patients with life-threatening infections, dosages up to 5 mg/kg/day may be administered in three or four equal doses. This dosage should be reduced to 3 mg/kg/day as soon as clinically indicated (TABLE I).

It is desirable to measure periodically both peak and trough serum concentrations of gentamicin when feasible during therapy to assure adequate but not excessive drug levels. For example, the peak concentration (at 30 to 60 minutes after intramuscular injection) is expected to be in the range of 4 to 6 mcg/mL. When monitoring peak concentrations after intramuscular or intravenous administration, dosage should be adjusted so that prolonged levels above 12 mcg/mL are avoided. When monitoring trough concentrations (just prior to the next dose), dosage should be adjusted so that levels above 2 mcg/mL are avoided. Determination of the adequacy of a serum level for a particular patient must take into consideration the susceptibility of the causative organism, the severity of the infection, and the status of the patient's host-defense mechanisms.

In patients with extensive burns, altered pharmacokinetics may result in reduced serum concentrations of aminoglycosides. In such patients treated with gentamicin, measurement of serum concentrations is recommended as a basis for dosage adjustment.

Children:    6 to 7.5 mg/kg/day. (2.0 to 2.5 mg/kg administered every 8 hours.)

Infants and Neonates:    7.5 mg/kg/day. (2.5 mg/kg administered every 8 hours.)

Premature or Full-Term Neonates One Week of Age or Less:    5 mg/kg/day. (2.5 mg/kg administered every 12 hours.)

The usual duration of treatment for all patients is 7 to 10 days. In difficult and complicated infections, a longer course of therapy may be necessary. In such cases, monitoring of renal, auditory, and vestibular functions is recommended, since toxicity is more apt to occur with treatment extended for more than 10 days. Dosage should be reduced if clinically indicated.

For Intravenous Administration

The intravenous administration of gentamicin may be particularly useful for treating patients with bacterial septicemia or those in shock. It may also be the preferred route of administration for some patients with congestive heart failure, hematologic disorders, severe burns, or those with reduced muscle mass. For intermittent intravenous administration in adults, a single dose of GARAMYCIN Injectable may be diluted in 50 to 200 mL of sterile isotonic saline solution or in a sterile solution of dextrose 5% in water; in infants and children, the volume of diluent should be less. The solution may be infused over a period of ½ to 2 hours.

The recommended dosage for intravenous and intramuscular administration is identical.

GARAMYCIN Injectable should not be physically premixed with other drugs, but should be administered separately in accordance with the recommended route of administration and dosage schedule.

DOSAGE FOR PATIENTS WITH IMPAIRED RENAL FUNCTION

Dosage must be adjusted in patients with impaired renal function to assure therapeutically adequate, but not excessive, blood levels. Whenever possible, serum concentrations of gentamicin should be monitored. One method of dosage adjustment is to increase the interval between administration of the usual doses. Since the serum creatinine concentration has a high correlation with the serum half-life of gentamicin, this laboratory test may provide guidance for adjustment of the interval between doses. The interval between doses (in hours) may be approximated by multiplying the serum creatinine level (mg/100 mL) by 8. For example, a patient weighing 60 kg with a serum creatinine level of 2.0 mg/100 mL could be given 60 mg (1 mg/kg) every 16 hours (2 × 8).

In patients with serious systemic infections and renal impairment, it may be desirable to administer the antibiotic more frequently but in reduced dosage. In such patients, serum concentrations of gentamicin should be measured so that adequate but not excessive levels result. A peak and trough concentration measured intermittently during therapy will provide optimal guidance for adjusting dosage. After the usual initial dose, a rough guide for determining reduced dosage at 8-hour intervals is to divide the normally recommended dose by the serum creatinine level (TABLE II). For example, after an initial dose of 60 mg (1.0 mg/kg), a patient weighing 60 kg with a serum creatinine level of 2.0 mg/100 mL could be given 30 mg every 8 hours (60 ÷ 2). It should be noted that the status of renal function may be changing over the course of the infectious process.

It is important to recognize that deteriorating renal function may require a greater reduction in dosage than that specified in the above guidelines for patients with stable renal impairment.

In adults with renal failure undergoing hemodialysis, the amount of gentamicin removed from the blood may vary depending upon several factors including the dialysis method used. An 8-hour hemodialysis may reduce serum concentrations of gentamicin by approximately 50%. The recommended dosage at the end of each dialysis period is 1 to 1.7 mg/kg depending upon the severity of infection. In children, a dose of 2 mg/kg may be administered.

The above dosage schedules are not intended as rigid recommendations but are provided as guides to dosage when the measurement of gentamicin serum levels is not feasible.

A variety of methods is available to measure gentamicin concentrations in body fluids; these include microbiologic, enzymatic, and radioimmunoassay techniques.

HOW SUPPLIED

GARAMYCIN Injectable, 40 mg per mL, for parenteral administration, is supplied in 2 mL (80 mg) vials, boxes of 25 (NDC 0085-0069-04).

GARAMYCIN Injectable is a clear, stable solution that requires no refrigeration.

Store between 2° and 30°C (36° and 86°F).

Schering Corporation

Kenilworth, NJ 07033 USA

Rev. 3/01 17150855

Copyright © 1968, 1992, 1994, 1996, Schering Corporation. All rights reserved.

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