Comparison of five methods for the assay of serum gentamicin

Development of HPLC methods for the determination of vancomycin in human plasma, mouse serum and bronchoalveolar lavage fluid

Two high-performance liquid chromatography methods utilizing a protein precipitation technique were developed to analyze vancomycin in human plasma, mouse serum and bronchoalveolar lavage (BAL) fluid. The mobile phase consisted of ammonium phosphate buffer with acetonitrile. A cross-matrix validation was performed to ensure that the mouse serum was comparable to the original biological matrix of human plasma. Murine BAL samples were run on a saline standard curve. For saline samples, the mobile phase from the human plasma study was used with the addition of 1M sodium hydroxide (0.2%) to avoid interfering peaks. A reversed-phase column was used with an ultraviolet detector set at 240 nm for human plasma and 198 nm for saline to increase peak size. The standard curves were liner over the ranges of 1 to 80 µg/mL for human plasma and 0.1 to 10 µg/mL for saline. These assays are simple, reproducible and accurate. These analytical techniques were successfully applied to analyze vancomycin concentrations in mouse serum and BAL samples.

Serum levels of ampicillin and gentamycin in neonates of varying gestational age

Serum concentrations of gentamycin and ampicillin were investigated at loading and in steady state in two groups of neonates, of 26-33 weeks and 34-40 weeks gestation. At loading the usual intravenous dose of gentamycin (2.5 mg/kg) was increased by 50%, the usual intravenous dose of ampicillin (50 mg/kg) by 100%. Gentamycin and ampicillin were administered subsequently at the same intervals, 12 h in the 34-40 weeks group, and 18 h in the 26-33 weeks group. Adequate serum levels were achieved from the first day of treatment. For practical reasons ampicillin and gentamycin can be administered subsequently at identical intervals also when the intervals exceed 12 h. The ideal dosing interval for gentamycin in very preterm neonates is 24 h. When treating small preterm and term neonates with an aminoglycoside, rapid serum concentration analyses should be available, and the treatment modified accordingly.

Determination of vancomycin in human serum by high-pressure liquid chromatography

A rapid, accurate, reverse-phase high-pressure liquid chromatographic procedure for vancomycin quantitation in human serum, cerebrospinal fluid, and peritoneal fluid was developed. This procedure involves a simple chemical extraction of the antibiotic and is suitable for each of these body fluids. The column and mobile phase used provided a good resolution of the vancomycin peak with a retention time of 6.1 min. The precision of the assay was within the requirement for a daily routine clinical application. Coefficients of variation for within-day reproducibility were 5.80 and 6.28%, respectively, for samples at 50 and 25 micrograms/ml, and for between-day reproducibility they were 11.4 and 11.1%, respectively. No interference was found with respect to beta-lactam and aminoglycoside antibiotics and many other currently used drugs, indicating a good specificity for the procedure. The detection limit of 100 ng/ml has proven to be sufficient for monitoring drug levels in serum obtained after usual dosages. Drug levels in 112 clinical serum specimens assayed by high-pressure liquid chromatography were regressed against the levels obtained for the same samples by radioimmunoassay and fluorescent polarization immunoassay. Correlation coefficients were 0.945 and 0.967, respectively, and were highly significant (alpha less than 0.001).

Comparison of the Beckman Auto ICS and the Syva Autolab 6000 for determination of gentamicin levels in serum

Two fully automated drug-monitoring systems, the Syva Autolab 6000 and the Beckman Auto ICS, were compared in terms of accuracy, precision, speed of operation, and cost effectiveness in the determination of gentamicin levels in serum. Within-run and between-run precision for both systems were acceptable (coefficient of variation, 2.0 to 6.9%), and patient sample comparisons resulted in an intermethod correlation coefficient of 0.96. When reference samples (prepared to contain 1.2 to 10 micrograms of gentamicin per ml) were assayed, the Syva Autolab 6000 obtained concentrations within 8% of expected values, whereas the Beckman Auto ICS reported values up to 17% higher than target values. In a time and cost comparison, reagent costs for the Beckman system were ca. 50% less than for the Syva Autolab 6000; the Syva system, however, determined patient results two to three times faster than the Beckman Auto ICS.

Determination of aminoglycosides in rat renal tissue by enzyme immunoassay

The enzyme-multiplied immunoassay technique for the determination of gentamicin or amikacin in serum was evaluated for use in rat renal tissue. After the addition of either gentamicin or amikacin to tissue homogenate, the assay of the supernatant showed a reduced recovery, depending on the amount of renal tissue present per milliliter of homogenate. The recovery was independent of the amount of aminoglycoside added. This reduction could be due to either protein binding or interference with the enzyme-multiplied immunoassay technique by substances released from the renal tissue. When the enzyme-multiplied immunoassay technique is used for aminoglycoside assay in renal tissue, care should be taken to minimize the amount of tissue present in the homogenate or to correct for the decreased recovery.

Comparison of radioimmunoassay and fluorescent polarization immunoassay for quantitative determination of vancomycin concentrations in serum

A new fluorescent polarization immunoassay (Abbott Laboratories, Diagnostics Division, North Chicago, Ill.) was compared with a standard radioimmunoassay (American Diagnostics Corp., Newport Beach, Calif.) in 34 patients being treated with vancomycin. A total of 123 serum samples were divided and quantitatively analyzed for vancomycin by both assay methods. The results obtained indicated that the two assay methods are comparable (y = 1.01x - 0.81; r = 0.99).

Comparison of radioimmunoassay and enzyme immunoassay methods in determining gentamicin pharmacokinetic parameters and dosages

Radioimmunoassay and enzyme immunoassay methods for analysis of serum gentamicin levels have been shown to be comparable. The purpose of this study was to determine if serum concentration-time data from the same patient assayed by radioimmunoassay and enzyme immunoassay would provide the same estimates for half-life, elimination rate constant, distribution volume, drug clearance, and gentamicin dose. A total of 103 pre- and postinfusion serum samples were obtained from 32 patients. The samples were divided and assayed by radioimmunoassay and enzyme immunoassay. Serum concentration-time data were fitted to a one-compartment model, and kinetic calculations were performed using the method of Sawchuk et al. (Clin. Pharmacol. Ther. 21:362-369, 1977). While good correlation was established between the two assay methods, significant (P less than 0.05) mean differences were seen in distribution volume (25%), gentamicin clearance (15%), and half-life (11%), using the quantitative data from both methods. Because of differences noted in these pharmacokinetic parameters, significant differences were also noted in dosage calculations. We conclude that there are differences in the pharmacokinetic parameters obtained using results from the radioimmunoassay and enzyme immunoassay. These differences also translate into significant differences between dosage recommendations when individualization of the gentamicin regimen is attempted.

Evaluation of the macro-vue latex agglutination test for quantitation of gentamicin in human serum

The Macro-Vue Card Test (Hynson, Wescott, and Dunning, Baltimore, Md.) for rapid quantitation of gentamicin in serum was compared with bioassay and radioimmunoassay procedures on sera from 100 patients. Regression analysis of paired results from the bioassay (using Klebsiella pneumoniae ATCC 27799) and the Macro-Vue Card Test indicated a correlation coefficient of 0.89, whereas comparing radioimmunoassay and Card Test results yielded a correlation coefficient of 0.83. The bioassay-radioimmunoassay correlation coefficient was 0.88. The data were further examined by grouping the sera of the patients into three categories based on therapeutic concentration ranges as follows: less than 2 micrograms/ml, subtherapeutic range; 2 to 8 micrograms/ml, therapeutic range; greater than 8 micrograms/ml, potentially toxic range. Of 100 specimen values, 81 fell into the same concentration range when bioassay and Card Test values were compared. Of the 19 disagreements, 12 were considered minor. Of 100 specimen values compared by radioimmunoassay and the Card Test, 88 fell into the same concentration range. Of the 12 disagreements, 6 were considered minor. Therefore, the Macro-Vue Card Test for gentamicin compared favorably with both the bioassay and radioimmunoassay procedures. The minimal time required to perform the Card Test (12 to 15 min) makes it attractive for situations in which immediate results are needed.

Comparison of different tobramycin assays

Three commercial available tobramycin assays, the fluorescent immunoassay (AMES), the Diagnostic Products Corp. radioimmunoassay, and the Nuclear Medical System radioimmunoassay, were compared with the microbiological assay and the chemical assay involving high-performance liquid chromatography. The results obtained with each assay were evaluated in terms of usefulness, reproducibility, and cost-effectiveness.

Assay of netilmicin, using enzyme immunoassay for gentamicin

A homogenous enzyme immunoassay for the quantitative determination of netilmicin in serum was developed. The procedure utilizes a commercially available assay for gentamicin (EMIT; Syva Co., Palo Alto, Calif.). The method was adapted to a microcentrifugal analyzer, and log-logit regression analysis was performed with a computer. The results of samples assayed by this method correlate well with microbioassay (r2 = 0.985) and radioimmunoassay (r2 = 0.986). This method is not only precise and accurate, but also very rapid and economical and compares favorably to other available methods of netilmicin assay.