Simplified high-performance liquid chromatographic method for determination of risperidone and 9-hydroxyrisperidone in serum from patients comedicated with other psychotropic drugs.

A HPLC method was developed for determination of risperidone and its therapeutically active main metabolite 9-hydroxyrisperidone in serum. After a single-step liquid-liquid extraction the analytes were separated on a C18 column and measured by UV detection at 280 nm. Inter-day coefficient of variation was <7% for both compounds at serum levels occurring in patients treated with ordinary doses. Studies of analytical interference showed that the most commonly coadministered antidepressants and benzodiazepines did not interfere. Some conventional low dose neuroleptics and clozapine did interfere, but this is of minor importance, because risperidone is intended as an alternative to these drugs.