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 CO2 atmosphere for the incubation. In the current study, it has been found that 10% CO2 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% CO2 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.
Footnotes
This work was supported by MSD (a part of Merck).
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
doi:10.1124/dmd.110.036988.
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ABBREVIATIONS:
- fup
- fraction unbound in plasma
- PPB
- plasma protein binding
- RED
- rapid equilibrium dialysis
- UPLC
- ultrapressure liquid chromatography
- DMSO
- dimethyl sulfoxide
- CV
- coefficient of variation.
- Received November 1, 2010.
- Accepted November 22, 2010.
- Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics
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