Sensitive gas-liquid chromatographic method for the determination of loratadine and its major active metabolite, descarboethoxyloratadine, in human plasma using a nitrogen-phosphorus detector.

A sensitive gas-liquid chromatographic (GLC) method was developed for the determination of loratadine, a long-acting tricyclic antihistamine, and its active metabolite, descarboethoxyloratadine, in human plasma. The method involved extraction with organic solvent at neutral and alkaline pH. The organic layer from the neutral pH extraction was evaporated to dryness, reconstituted and injected into the GLC system. On the other hand, to the organic layer from the alkaline pH extraction trifluoroacetic anhydride was added. Following addition of H2O, the mixture was centrifuged and the organic layer was evaporated to dryness, reconstituted and injected onto the GLC system that was equipped with a nitrogen specific detector and a fused-silica capillary column. The linearity for both loratadine and descarboxyloratadine were demonstrated with r > or = 0.998 at concentrations ranging from 0.1 to 30 ng/ml. The results showed that the GLC method was accurate (bias < or = 12%) and precise (coefficient of variation, C.V., < or = 12%) for loratadine and descarboethoxyloratadine. The limit of quantitation was 0.1 ng/ml for loratadine with a C.V. of 9.2% and for descarboethoxyloratadine with a C.V. of 5.3%. The GLC method described has been demonstrated to be useful for the determination of loratadine and descarboethoxyloratadine in plasma samples of pediatric volunteers following oral administration of a single dose of 10 mg of loratadine syrup.