The distribution of halofenate in plasma: a comparative analysis using Scatchard vs. stepwise association constants

The distribution of Halofenate between the free and albumin bound forms was calculated by the use of two computer programs using both Scatchard association constants for a 3,3,7 model, and six stepwise equilbrium constants over a range of drug concentrations reported in man. The calculations, using either set of constants, showed that only 0.3 to 0.5% of the drug would be free. Using Scatchard association constants, it was estimated that 92 to 95% of the drug would be bound by the high affinity set of sites, and lesser amounts by sites of lesser affinity. A more complex pattern of distribution was obtained with the stepwise equilibrium constants. At low concentrations of Halofenate the complex with one mole of drug/mole of protein was most abundant and at the highest concentration studied the complex with two moles of drug/mole of protein was most abundant.