Simultaneous determination of duloxetine and 4-hydroxy duloxetine glucuronide in human plasma and back-conversion study

To develop an LC-MS/MS method for simultaneous determination of duloxetine and its metabolite, 4-hydroxy duloxetine glucuronide (4HDG) in human plasma and to investigate the potential back-conversion of 4HDG to duloxetine using stability study. The LC-MS/MS method was validated according to the EMA and USFDA Bioanalytical Method Validation Guidelines and applied to pilot bioequivalence study. The method validation results were within the acceptance limits. The stability study and incurred sample reanalysis results ruled out the occurrence of back-conversion. The study highlighted the conduct of back-conversion test and the advantages of LC-MS/MS method in terms of sensitivity, specificity and low consumption of organic solvents.