Comparison of gentamicin immunoassays using univariate and multivariate analyses

Area of Science:

• Clinical Chemistry
• Pharmacokinetics
• Analytical Toxicology

Background:

• Accurate measurement of gentamicin concentrations is crucial for effective therapeutic drug monitoring.
• Different immunoassay methods may yield variable results, impacting clinical decisions.
• Understanding assay differences and influencing patient factors is essential for optimizing gentamicin therapy.

Purpose of the Study:

• To compare gentamicin concentrations, pharmacokinetic parameters, and calculated doses between enzyme multiplied immunoassay (EMI) and fluorescence polarization immunoassay (FPIA).
• To assess the association between patient factors and the discrepancies observed between the two assay methods.

Main Methods:

• Comparison of gentamicin measurements in 79 patient samples using EMI and FPIA.
• Calculation and comparison of pharmacokinetic parameters (elimination rate constant, volume of distribution, clearance) and drug doses.
• Statistical analysis (univariate and multivariate) to identify patient factors associated with assay result differences.

Main Results:

• Gentamicin concentrations were significantly lower with EMI compared to FPIA in most samples (71/79).
• Mean pharmacokinetic parameters and calculated doses were 10-20% higher when determined by EMI versus FPIA.
• Dosing intervals calculated from EMI and FPIA data often differed, with variations dependent on interval length.

Conclusions:

• Significant differences exist between EMI and FPIA for gentamicin analysis in a clinical setting.
• These assay-related discrepancies can potentially lead to toxic or subtherapeutic gentamicin dosing.
• Patient-specific factors, including renal function and co-administered medications, may contribute to observed assay differences.