Effective on-line extraction of drugs from plasma using a restricted-access media column in column-switching HPLC equipped with a dilution system: Application to the simultaneous determination of ER-118585 and its metabolites in canine plasma

The present paper describes the on-line extraction of drugs in plasma using a restricted-access media (RAM) column in a column-switching high performance liquid chromatography (HPLC) apparatus that was equipped with an on-line dilution system. The use of a six- to eightfold on-line dilution ratio for plasma samples resulted in almost 100% recovery of both acidic and basic drugs from plasma. It was found that the relationship between the on-line dilution times and drug recovery efficiencies from plasma was explained in terms of the binding constant between the drug and albumin. The applicability of column-switching HPLC with an on-line dilution system and the effectiveness of the extraction procedure were confirmed by a simultaneous determination of the basic compound, ER-118585, and its metabolites in canine plasma.