Serum gentamicin assay by a radiometric procedure

Area of Science:

• Clinical Chemistry
• Microbiology
• Pharmacokinetics

Background:

• Accurate determination of gentamicin serum levels is crucial for therapeutic drug monitoring.
• Existing microbiologic assays and radioimmunoassay (RIA) methods have limitations in speed or cost.
• Radiometric methods offer potential for rapid and sensitive drug level determination.

Purpose of the Study:

• To evaluate a new radiometric (BACTEC) assay for gentamicin serum level determination.
• To compare the BACTEC assay's performance against established microbiologic assays and RIA.
• To assess the accuracy, speed, and reproducibility of the BACTEC method.

Main Methods:

• A 14C-urea substrate and Proteus species culture were used in the BACTEC assay.
• Gentamicin levels in serum were determined using the BACTEC assay, three non-radiometric microbiologic assays, and RIA.
• Assay performance was compared across different gentamicin concentration ranges.

Main Results:

• The BACTEC assay was found to be simple, fast, and reproducible.
• At gentamicin concentrations < 4 microgram/ml, BACTEC accuracy was comparable to other assays.
• At gentamicin concentrations > 4 microgram/ml, BACTEC showed significant differences, reading lower than RIA and other assays.

Conclusions:

• The BACTEC assay is a viable alternative to RIA for laboratories with radiometric equipment, especially for batch processing.
• Due to cost, BACTEC is less practical than rapid, inexpensive microbiologic assays for routine gentamicin monitoring.
• The BACTEC assay's accuracy is concentration-dependent, requiring careful consideration for therapeutic drug monitoring.