Determination of the antiallergenic agent, trans-3-[6-(methylthio)-4-oxo-4H-quinazolin-3-yl]-2-propenoic acid, in plasma by high-performance liquid chromatography.

A rapid and selective high-performance liquid chromatographic (HPLC) assay was developed for the determination of the antiallergenic compound, trans-3-[6-(methylthio)-4-oxo-4H-quinazolin-3-yl]-2-propenoic acid, [I], in plasma. The assay involves acetonitrile protein precipitation followed by the analysis of an aliquot of the protein-free fraction by reversed-phase HPLC with fluorescence detection (excitation at 245 nm, with emission greater than 418 nm). The overall recovery of [I] from plasma was 103 +/- 10%. The sensitivity limit of the assay was 0.125 microgram/ml of plasma. The analogous compound, trans-3-[6-[(1-methylethyl)thio]-4-oxo-4H-quinazolin-3-yl]-2-propenoic acid, [II], is used as the internal standard. The assay was used to monitor the plasma concentration--time fall-off profile of [I] in the dog and in man. The stability of [I] was demonstrated in dog plasma on long-term storage for up to 180 days at -17 degrees C and -70 degrees C.