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Test Code TOBT TOBRAMYCIN, TROUGH

Important Note

Caution:

Concentrations of β-lactam antibiotic (penicillins and cephalosporins) at therapeutic levels may inactivate tobramycin in vitro.  Specimens from patients receiving β-lactam antibiotics should be assayed immediately or stored frozen until assayed.


Results for samples from patients receiving Amikacin, Dibekacin, Gentamicin or kanamycin may be falsely elevated due to creoss-reactivity in this assay (Amikacin, approximately 1%; Dibekacin, approximately 55%;Gentamicin, approximately 2% and Kanamycin, u to 23%)

Methodology

Homogeneous Enzyme Immunoassay

Useful For

Monitoring adequacy of clearance of tobramycin near the end of a dosing cycle.

Tobramycin is an antibiotic used to treat life-threatening blood infections by gram-negative bacilli, particularly Citrobacter freundii, Enterobacter (all species), Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Providencia stuartii, Pseudomonas aeruginosa, and Serratia species. It is often used in combination with beta-lactam therapy.

A tobramycin minimum inhibitory concentration (MIC) of less than 4.0 mcg/mL is considered susceptible for gram-negative bacilli, while a MIC of greater than 8.0 mcg/mL is considered resistant.

 

Ototoxicity and nephrotoxicity are the primary toxicities associated with tobramycin. This risk is enhanced in presence of other ototoxic or nephrotoxic drugs. Monitoring of serum levels and symptoms consistent with ototoxicity is important. For longer durations of use, audiology/vestibular testing should be considered at baseline and periodically during therapy.

Specimen Requirements

Preferred:

Specimen Type:         Serum

Container/Tube:        Serum Gel Tube

Specimen Volume:    0.5 mL serum (minimum 0.25 mL)

Alternate:         Serum, Plain red-top tube

                          Heparin Plasma, Green top gel tube

 

Collection Instructions:

  1. Draw no more than 30 minutes before next schedule dose.
  2. Spin down within 1 hour of draw.
  3. Store specimens refrigerated until assayed.

Day(s) Test Set Up

Monday through Sunday

Specimen Stability

Refrigerated

Reference Values

Conventional dosing:                         < 2.0 mcg/mL

High-dose extended interval dosing: < 1.0 mcg/mL

Critical Level:                                      > 2.0 mcg/mL

Performing Laboratory

Logan Health Medical Center Laboratory

Test Classification and CPT Coding

80200