Use of Serum Ultrafiltrate in the Serum Dilution Test

Abstract

Although pooled human serum diluent is advocated in the serum dilution test, its use may compensate for protein binding defects in patients and yield nonrepresentative titers. To test this hypothesis, comparison was made of serum ultrafiltrate (molecular weight cutoff less than or equal to 30,000) serially diluted into either pooled serum ultrafiltrate or Mueller-Hinton broth with patient serum samples diluted into pooled human serum in 111 assays from 55 patients and 6 volunteers. Of 111 bactericidal titers in ultrafiltrate and/or Mueller-Hinton broth, 101 were within a single twofold dilution of titers in pooled human serum. Nine of 10 discordant titers involved highly bound drugs and were usually higher in ultrafiltrate than in pooled human serum. In seven additional volunteers with renal failure, titers in ultrafiltrate and in each volunteer's serum were higher than those diluted in pooled human serum (P = .002). Recommended methods using pooled serum diluent may not accurately predict actual bactericidal titers in patients with abnormal protein binding.

Clinical Pharmacology of the Fluoroquinolones: Studies in Human Dynamic/Kinetic Models

“…AUIC may be measured as the reciprocal of the serum inhibitory titer (SIT) versus time curve; for SIT testing, ultrafiltrates of patient serum have proven best [18], in addition to the performance of timed kill curves in which antibiotic carryover is eliminated by the removal or inactivation of antibiotic. When time-to-bacterial eradication was modeled versus AUIC, 3 significantly distinct patient groups were identified ( ; P !…”

Pharmacodynamic Interactions of Antibiotics Alone and in Combination

“…From these investigations, there is evidence that AUIC trate inhibitory testing was performed as described by Leggett can predict microbiological and clinical cure rates [15 -17]. et al [37]. The individual pharmacokinetic parameters for each The challenge is to use the AUIC method effectively to drug were estimated with use of ADAPT II (Biomedical Simucharacterize combination therapy as well as it has done with lations Resource, Los Angeles) and the MAP Bayesian algosingle agents.…”

Influence of Assay Methodology on the Measurement of Free Serum Ceftriaxone Concentrations

“…In conclusion, the determination of free ceftriaxone levels in humans is dependent upon the assay technique used. Use of methods that overestimate the free-drug concentration may result in misinterpretation of data (9) or inappropriate calculations of dosing regimens (12). Further, the magnitude of drug-protein binding varies from animal species to animal species.…”

“…Although only free drug is microbiologically active (4), National Committee for Clinical Laboratory Standards guidelines are still set with total drug levels. Overestimates of the amount of highly protein-bound drugs to be administered can ensue, particularly in hypoalbuminemic states related to illness or renal impairment (8,9). Techniques to determine the amount of free drug in plasma include agar diffusion bioassay, protein precipitation with subsequent highperformance liquid chromatography (HPLC) assay of supernatant, and membrane ultrafiltration with HPLC assay of the ultrafiltrate (4).…”