[HPLC-determination of loratadine and its active metabolite descarboethoxyloratadine in human plasma].

The quantitative determination of loratadine (1) and its active metabolite descarboethoxyloratadine (2) is described. Because of the high difference in polarity between 1 and 2, the two analytes were determined in two HPLC-systems separately. As internal standards propyl-4-(8-chloro-5,6-dihydro-11H-benzo-[5,6]-cyclohepta-[1,2-b]- pyridin-11-ylidin)-1-piperidincarboxylate (3) and 1-ethyl-4-(8-chloro-5,6-dihydro-11H-benzo-[5,6]-cyclohepta- [1,2-b]-pyridine-11-ylidin)-piperidine (4) were used for 1 and 2, respectively. After extraction with organic solvents from 1 ml plasma, 1 and 2 were reextracted with diluted phosphoric acid from the organic phase. Chromatographic separation on a RP-18 column and fluorescence detection allowed a sufficiently sensitive determination of 1 and 2 in plasma with a lower limit of quantitation of 0.5 ng/ml for both analyts. The method was successfully applied to human plasma samples from 16 subjects after oral administration of 20 mg 1.