High‐performance liquid chromatographic analysis, plasma protein binding and red blood cell partitioning of phenprobamate

Abstract

A new high-performance liquid chromatographic procedure for the analysis of phenprobamate, a skeletal muscle relaxant in biologic fluids was developed. The method used a C18 reverse phase column, a mobile phase of methanol/acetonitrile/water (33:15:52), and UV detection at 215 nm. The assay procedure was applied to the determination of phenprobamate binding to rat and human plasma proteins using the equilibrium dialysis method. In addition, the red blood cell/plasma partitioning was determined in the whole blood of rats and humans. Phenprobamate exhibited a moderate binding to plasma proteins of rat (74.3 +/- 2.2 per cent) and human (80.5 +/- 1.1 per cent). The protein binding was concentration-independent in the range of 10 to 80 micrograms ml-1. Phenprobamate binding to plasma proteins was also determined in the presence of 10 micrograms ml-1 acetaminophen. The protein binding of phenprobamate was not significantly altered by acetaminophen (74.4 +/- 0.6 per cent for rat plasma; 75.7 +/- 1.6 per cent for human plasma). The distribution ratios of phenprobamate between the red blood cells and plasma were greater than unity, 1.86 and 1.59 in rat and human, respectively, indicating a preferential partitioning of the drug in the red blood cells.

A novel liquid chromatography/tandem mass spectrometry based depletion method for measuring red blood cell partitioning of pharmaceutical compounds in drug discovery

“…The RBC partitioning of phenoprobamate is predominately associated with fast passive diffusion, 6,7 while that of acetazolamide is controlled by a composite of fast passive diffusion and, to a larger extent, a slower kinetic process associated with in-cell protein binding. Figure 2 shows the time course of the partitioning of the two compounds measured by the new method.…”

Selective and sensitive determination of bis(7)‐tacrine, a high erythrocyte binding acetylcholinesterase inhibitor, in rat plasma by high‐performance liquid chromatography–tandem mass spectrometry

“…Fraction of drug in erythrocytes = 1 − 0.55 × C p /C blood (Sun et al, 1987) where C p and C blood represent the plasma concentration and the blood concentration of the drug respectively.…”

Technical Challenges and Recent Advances of Implementing Comprehensive ADMET Tools in Drug Discovery

“…With this approach, the fraction of drug unbound in plasma ( f up ) equals the concentration of drug measured in buffer (which mirrors the free con- When K RBC/PL ∼ 1, this is an indication that the test drug distributes equally between the blood cell fraction and plasma and reaffi rms that plasma is, in fact, a fair, representative matrix from which to derive PK profi les. When K RBC/PL >> 1, this may be evidence that the test drug favors uptake by, or association with, the RBC fraction (Sun et al, 1987 ;Yu et al, 2005 ).…”