Gentamicin Injection 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
Children: 6 to 7.5 mg/kg/day. (2 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.)
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 3 to 5 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.
The usual duration of treatment 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, a single dose of Gentamicin Injection may be diluted in 0.9% Sodium Chloride Injection or in 5% Dextrose Injection. The solution may be infused over a period of one-half to two hours.
The recommended dosage for intravenous and intramuscular administration is identical.
Gentamicin Injection 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. In adults, 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 mg/100 mL could be given 60 mg (1 mg/kg) every 16 hours (2 x 8). These guidelines may be considered when treating infants and children with serious renal impairment.
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 eight-hour intervals is to divide the normally recommended dose by the serum creatinine level (Table 3). For example, after an initial dose of 20 mg (2 mg/kg), a child weighing 10 kg with a serum creatinine level of 2 mg/100 mL could be given 10 mg every eight hours (20 ÷ 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.
DOSAGE ADJUSTMENT GUIDE
FOR PATIENTS WITH RENAL IMPAIRMENT
(Dosage at Eight-Hour Intervals
After the Usual Initial Dose)
1.1 to 1.3
70 to 100
1.4 to 1.6
55 to 70
1.7 to 1.9
45 to 55
2 to 2.2
40 to 45
2.3 to 2.5
35 to 40
2.6 to 3
30 to 35
3.1 to 3.5
25 to 30
3.6 to 4
20 to 25
4.1 to 5.1
15 to 20
5.2 to 6.6
10 to 15
6.7 to 8
In patients 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 eight-hour hemodialysis may reduce serum concentrations of gentamicin by approximately 50%. In children, the recommended dose at the end of each dialysis period is 2 to 2.5 mg/kg depending upon the severity of the infection.
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 are available to measure gentamicin concentrations in body fluids; these include microbiologic, enzymatic and radioimmunoassay techniques.
Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.