amikacin in serum/plasma
Reference interval
Strong correlations have been shown between serum levels & both therapeutic effect & toxicity in specific patient types. Peak serum levels of amikacin in the range of 20 to 25 ug/mL are suggested for optimal therapeutic effectiveness. Persistently elevated peak concentration (30-35 ug/mL) have been shown to cause renal & central nervous system toxicity. Trough levels offer a more discrete indication of impending toxicity since they more closely correspond to tissue levels & are less affected by sampling errors. Slowly rising trough levels have been shown to correspond to tissue accumulation of the drug, & trough levels greater> 10 ug/mL have been associated with renal failure in some patients.
Principle
The TDx Amikacin assay is a reagent system for the quantitative measurement of amikacin, an aminoglycoside antibiotic drug, in serum or plasma. The measurements obtained are used in the diagnosis & treatment of amikacin overdose & in monitoring levels of amikacin to ensure appropriate therapy. The Amikacin assay utilizes Fluorescence Polarization Immunoassay technology as described in the TDx Procedure on page 1.
Clinical significance
Amikacin is effective in the treatment of serious gram-negative infections & is particularly useful in those involving strains resistant to all the other aminoglycosides. Amikacin is probably the aminoglycoside of first choice when gentamicin resistance is strongly suspected. As with other aminoglycosides, there is a narrow margin between therapeutic effectiveness & toxicity. Amikacin should be used with caution in patients with depressed renal function. Serum levels should be monitored, applying the concepts developed for gentamicin.
Specimen
Collect blood samples by venipuncture following established good laboratory practices. If the sample is obtained through the infusion set, flush the line thoroughly with saline before taking the blood sample. With some exceptions, any anticoagulant may be used to collect plasma for analysis. Serum, as well as plasma, may be used for most assays. It is very important that the physician be informed of the times of sample collection & dose administration; this information should be supplied to the laboratory with each sample & reported with the results of each test. Samples derived from blood should be refrigerated upon collection & stored frozen (-20 degrees Celsius or colder) if not analyzed within 24 hours. Complete mixing of each thawed sample is required before analysis.
Urine samples must be collected in clean, previously unused containers. It is recommended that samples should be refrigerated upon collection & stored frozen if not analyzed within 48 hours.
CSF & amniotic fluid samples should be obtained using standard collection procedures.
Fibrin threads or large particles which could block the probe should not be pipetted or poured into the sample well. After sample transfer, assure there are no bubbles or foam present in the sample well. Remove bubbles or foam prior to running.
Fluorescein is a constituent of all FPIA reagent systems. Patient samples containing fluorescent compounds may interfere with these TDx methodologies resulting in high blank intensity readings & low net intensities. If patient samples cannot be diluted below the maximum background value an alternate methodology should be used.
Automatic serum blank readings reduce optical interferences from grossly icteric, hemolyzed or lipemic samples. Serum blanks are automatically subtracted by the TDx analyzer before final results are printed, when required by the specific assay mode. Minimum sample volume is 50 uL.
The concentration range of the TDx Amikacin Calibrators (0-50 ug/mL) is adequate to accurately determine the amikacin concentration in most of the patient samples encountered. Occasionally samples contain amikacin in concentrations > the highest calibrator (50 ug/mL). To accurately determine the drug concentration in these samples, refer to the Dilution Protocol outlined in the TDx Procedure.
The lowest measurable level is defined as that concentration which can be distinguished from zero with 95% confidence; it was determined to be 0.8 ug/mL.
Sources of Error:
- Abnormal levels of total protein, (0-10 g/dL), lipid, (0-531 mg/dL triglycerides & 0-492 mg/dL cholesterol), hemoglobin (0-0.86 g/dL), icteric samples (0-15 mg/dL total bilirubin) & heparin (0-354 units/mL) result in less than a 5% error in quantitating a sample with the Amikacin assay when run on the analyzer.
- Patient samples which contain Kanamycin A, Kanamycin B, 3,4, Dideoxykanamycin B or Tobramycin will yield falsely elevated values for amikacin. However, these drugs are not usually coadministered with amikacin. High concentration of penicillins or cephalosporins have been shown to inactivate aminoglycosides in vitro. The degree of inactivation is dependent on the particular aminoglycoside being measured, the type & concentration of the penicillin or cephalosporin that is also present & the storage conditions of the sample. Samples from patients receiving additional antibiotics of these types should be assayed immediately or stored frozen.
More general terms
More specific terms
- amikacin free in serum/plasma
- amikacin in serum/plasma peak
- amikacin in serum/plasma post dialysis
- amikacin in serum/plasma trough
Additional terms
References
- ↑ ABBOTT TDx System Operation Manual Abbott Laboratories, Diagnostics Division, Abbott Park, IL
- ↑ Amikacin, Random Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0090015.jsp
- ↑ Amikacin Peak Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0090295.jsp
- ↑ Amikacin Trough Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0090300.jsp