title: Control and measurement of plasma pH in equilibrium dialysis: influence on drug plasma protein binding.
abstract: Past publications have highlighted the influence of postdialysis plasma pH on the measured fraction unbound in plasma (fup). There is disparity in the industry as to which of two main methods is more suitable for controlling postdialysis plasma pH: the use of either a stronger buffer or a CO(2) atmosphere for the incubation. In the current study, it has been found that 10% CO(2) could be too high for the buffering capacities of both 100 mM sodium phosphate (pH 7.40 decreased to pH 6.90 after a 6-h incubation) and plasma (decreased below pH 7.40 after a 6-h incubation). To provide appropriate control over the postdialysis plasma pH, for a range of species, it is proposed that a standard phosphate buffer strength (100 mM) and pH (7.40) in combination with a 5% CO(2) atmosphere be used for equilibrium dialysis. Furthermore, statistically significant differences in fup values obtained with a pH difference of less than 0.32 pH unit have been demonstrated. An acceptance range for postdialysis plasma pH in routine in vitro fup screening assays of pH 7.40 ± 0.10 is recommended.
authors.affiliation: DMPK and Bioanalysis, Department of Pharmacology, MSD, Newhouse, Scotland, United Kingdom. ruthecurran@hotmail.com
authors.forename: Ruth E
authors.initials: RE
authors.lastname: Curran
authors.forename: Christopher R J
authors.initials: CR
authors.lastname: Claxton
authors.forename: Laura
authors.initials: L
authors.lastname: Hutchison
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Harradine
authors.forename: Iain J
authors.initials: IJ
authors.lastname: Martin
authors.forename: Peter
authors.initials: P
authors.lastname: Littlewood
mesh_terms: D000818:Animals; D001798:Blood Proteins / Q000378:metabolism*; D002021:Buffers; D002245:Carbon Dioxide; D055598:Chemical Phenomena; D003956:Dialysis; D004285:Dogs; D004353:Drug Evaluation, Preclinical / Q000379:methods; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008252:Macaca fascicularis; D051379:Mice; D009994:Osmolar Concentration; D004364:Pharmaceutical Preparations / Q000097:blood* / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D015203:Reproducibility of Results
chemical_list: D001798:Blood Proteins; D002021:Buffers; D004364:Pharmaceutical Preparations; D002245:Carbon Dioxide