In vitro evaluation of a vancomycin radioimmunoassay and observations on vancomycin pharmacokinetics in dialysis patients

Determination of Vancomycin in Human Serum by Cyclodextrin-Micellar Electrokinetic Capillary Chromatography (CD-MEKC) and Application for PDAP Patients

A simple and sensitive cyclodextrin-micellar electrokinetic capillary chromatography (CD-MEKC) method with UV detection was developed and validated for the determination of vancomycin (VCM) in serum. The separation was achieved in 14 min at 25 °C with a fused-silica capillary column of 40.2 cm × 50 mm i.d. (effective length 30.2 cm) and a run buffer containing 25 mM borate buffer with 50 mM sodium dodecylsulfonate (SDS) (pH 9.5) and 2% sulfobutyl-β-cyclodextrin (sulfobutyl-β-CD). Under optimal conditions for biological samples, good separations with high efficiency and short analysis time were achieved. Several parameters affecting the drug separation from biological matrices were studied, including buffer types, concentrations, and pHs. The methods were validated over the range of 0.9998-99.98 µg/mL. Calibration curves of VCM also showed good linearity (r² > 0.999). Intra- and interday precisions (relative standard deviation, RSD) were less than 5.80% and 7.38%, and lower limit of quantification (LLOQ) were lower than 1.0 μg/mL. The mean recoveries ranged between 84.03% and 91.69%. The method was successfully applied for monitoring VCM concentrations in serum of patients with peritoneal dialysis-associated peritonitis (PDAP). The assay should be applicable to pharmacokinetic studies and routine therapeutic drug monitoring of this drug in serum.

Biopsy-proved acute tubulointerstitial nephritis and toxic epidermal necrolysis associated with vancomycin

A 70-year-old man receiving vancomycin for a methicillin-resistant Staphylococcus aureus (MRSA) abscess developed a drug-induced hypersensitivity reaction with rash, eosinophilia, and acute renal failure requiring dialysis. Renal biopsy revealed diffuse and marked interstitial and tubular infiltration by mononuclear cells and eosinophils; acute tubulointerstitial nephritis (TIN) was diagnosed. The rash progressed to erythema multiforme major after rechallenge with vancomycin in the setting of MRSA peritoneal catheter-related peritonitis and then to fatal toxic epidermal necrolysis in the setting of steroid taper and persistent serum vancomycin levels. This case further implicates vancomycin as a drug that infrequently can cause severe acute TIN and exfoliative dermatitis. When a renally excreted drug such as vancomycin is administered, serum drug levels should be serially monitored and high-dosage steroids be maintained or tapered slowly until serum drug levels become undetectable.

Vancomycin serum protein binding determination by ultrafiltration

Sixty-two serum concentrations were obtained from 12 infected patients enrolled in a vancomycin pharmacokinetic study. Both unbound and total serum vancomycin concentrations were measured using ultrafiltration and a commercial fluorescent polarization immunoassay. Ultrafiltrates were obtained by centrifugation at 1000 X g for ten minutes at room temperature and their assay indicated a range in protein binding from 7.9 to 71 percent. The mean protein binding (mean +/- SD) was 41.95 +/- 14.15 percent. No measurable adsorption of vancomycin onto the ultrafiltration membrane was noted. Orthogonal regression of unbound versus total vancomycin concentrations was described by the equation y = 0.597x-0.362 with a correlation coefficient of 0.948.

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).