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Gentamicin
MessagePerforming Lab: Regions, Westfields
Test Code
0498
Alias/See Also
Sunquest: GENT
CPT Codes
80170
Preferred Specimen
0.2 mL Lithium Heparin Plasma (light green-top) tube
Minimum Volume
0.1 mL
Other Acceptable Specimens
Serum separator (gold-top), Lithium Heparin (light green-top) on ICE, Red, Red/Gray, EDTA plasma (lavender-top)
Instructions
Collection:
For patients receiving gentamicin via conventional dosing methods peak and trough drug monitoring should begin after a steady state is achieved (usually after 3–4 doses). Samples for peak concentrations should be collected 60–90 minutes after intravenous infusion.
Samples for trough concentrations should be collected within 30 minutes of the next dose.
For patients receiving gentamicin via a pulse-dosing method, monitoring can begin after the first dose because steady-state conditions are not obtained. Monitoring strategies will vary with dosing regimens.
When using pulse dosing nomograms, a timed sample should be collected 8–12 hours after completion of drug infusion in order to determine the subsequent dosing interval. This should be repeated at 3–7 day intervals or more frequently as warranted.
For patients receiving gentamicin via conventional dosing methods peak and trough drug monitoring should begin after a steady state is achieved (usually after 3–4 doses). Samples for peak concentrations should be collected 60–90 minutes after intravenous infusion.
Samples for trough concentrations should be collected within 30 minutes of the next dose.
For patients receiving gentamicin via a pulse-dosing method, monitoring can begin after the first dose because steady-state conditions are not obtained. Monitoring strategies will vary with dosing regimens.
When using pulse dosing nomograms, a timed sample should be collected 8–12 hours after completion of drug infusion in order to determine the subsequent dosing interval. This should be repeated at 3–7 day intervals or more frequently as warranted.
Transport Temperature
Refrgerated
Specimen Stability
Room Temperature: 2 hours
Refrigerated: 7 days
Frozen: 14 days
Refrigerated: 7 days
Frozen: 14 days
Methodology
Two-point Rate
Setup Schedule
Daily
Report Available
Same day.
Limitations
Results for samples from patients receiving netilimicin or sisomicin, aminoglycosides structurally related to gentamicin, may be falsely elevated due to cross-reactivity in this assay .
Concentrations of ß-lactam antibiotics (penicillins and cephalosporins) at therapeutic levels may inactivate gentamicin in vivo and in vitro. Specimens from patients receiving ß-lactam antibiotics (penicillins and cephalosporins) must be analyzed immediately upon receipt or stored frozen to prevent in vitro inactivation of gentamicin.
Concentrations of ß-lactam antibiotics (penicillins and cephalosporins) at therapeutic levels may inactivate gentamicin in vivo and in vitro. Specimens from patients receiving ß-lactam antibiotics (penicillins and cephalosporins) must be analyzed immediately upon receipt or stored frozen to prevent in vitro inactivation of gentamicin.
Reference Range
Trough: <2.0 µg/mL
Peak: 4.0- 10.0 µg/mL
Critical: >= 12.0 µg/mL
Peak: 4.0- 10.0 µg/mL
Critical: >= 12.0 µg/mL
Clinical Significance
Gentamicin is used in the treatment of serious infections caused by susceptible strains of gram-negative microorganisms and particular gram-positive organisms that are resistant to less toxic antibiotics. Gentamicin is safe and effective only in a narrow range of concentrations for a given indication. Exposure to high gentamicin concentrations for a prolonged period may cause renal impairment or ototoxicity. Serum or plasma gentamicin measurements are used in the diagnosis and treatment of gentamicin overdose and in monitoring levels of gentamicin to ensure appropriate therapy.
