title: Determination of free vancomycin, ceftriaxone, cefazolin and ertapenem in plasma by ultrafiltration: impact of experimental conditions.
abstract: Ultrafiltration is a rapid and convenient method to determine the free concentrations of drugs. In the present work, we aimed to develop an ultrafiltration method which is appropriate for routine determination of the free fraction of vancomycin and highly protein bound beta-lactams such as ertapenem, ceftriaxone and cefazolin in plasma from intensive care unit patients. Different filter types and experimental conditions (molecular weight cut-off, centrifugal force and time, pH, temperature) were evaluated and found to have influence on the result. In the final protocol, serum or plasma was buffered to pH 7.4-7.5, ultrafiltered at 1000×g at 37°C for 20min using Nanosep Omega 10K filters and subsequently analysed for the antibiotics by RP-HPLC with UV detection. The data from our investigation suggest to aim physiological conditions, i.e. 37°C and pH 7.4, and low to moderate relative centrifugal forces in order to get reliable results. With regard to the chromatographic separation, modulation of the pH in the range of 2.5-7.0 allows to determine several beta-lactams isocratically and/or to avoid interferences by co-administered drugs.
authors.affiliation: Hospital Pharmacy, University Hospital Regensburg, Franz-Josef-Strauß Allee 11, 93053 Regensburg, Germany; Department of Pharmaceutical Biology, University of Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kratzer
authors.affiliation: Department of Internal Medicine I, University Hospital Regensburg, Franz-Josef-Strauß Allee 11, 93053 Regensburg, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Liebchen
authors.affiliation: Department of Internal Medicine I, University Hospital Regensburg, Franz-Josef-Strauß Allee 11, 93053 Regensburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Schleibinger
authors.affiliation: Department of Anesthesiology and Intensive Care, Charité University Hospital Berlin - Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany.
authors.forename: Martin G
authors.initials: MG
authors.lastname: Kees
authors.affiliation: Department of Pharmacology, University of Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany. Electronic address: frieder.kees@ur.de.
authors.forename: Frieder
authors.initials: F
authors.lastname: Kees
mesh_terms: D002437:Cefazolin / Q000097:blood*; D002443:Ceftriaxone / Q000097:blood*; D004355:Drug Stability; D000077727:Ertapenem; D006801:Humans; D011485:Protein Binding; D014462:Ultrafiltration / Q000379:methods; D014640:Vancomycin / Q000097:blood*; D047090:beta-Lactams / Q000097:blood*
chemical_list: D047090:beta-Lactams; D014640:Vancomycin; D002443:Ceftriaxone; D000077727:Ertapenem; D002437:Cefazolin
keywords: Beta-lactam; HPLC; Protein binding; Relative centrifugal force; Temperature; pH