Background: Duloxetine (DL) is a selective serotonin and norepinephrine reuptake inhibitor.
The drug is used in the treatment of major depression, anxiety, pain related to diabetic peripheral neuropathy
and stress urinary incontinence.
Objective: This study described, for the first time, the development and validation of a highly selective
and sensitive microemulsion liquid chromatography-fluorescence (MELC-FL) method with low environmental
pollution and without extraction steps for the simultaneous quantification of DL, and its two
main metabolites; 5-hydroxy-6-methoxy duloxetine (5-HDL) and 4-hydroxy duloxetine glucuronide (4-
HDLG) in plasma.
Methods: The studied analytes and methyl paraben (an internal standard) were detected using excitation
and emission wavelengths of 280 and 340 nm, respectively. The analysis was performed on Water
Symmetry C18 analytical column (100 Å, 150 mm x 3.9 mm, 5 µm) by directly injecting the plasma
after appropriate dilution with microemulsion mobile phase. Total analytical run time was 4 min.
Results: The MELC-FL method was statistically validated according to the FDA guidelines for bioanalytical
methods for linearity, accuracy, precision, specificity, robustness, and stability. Linear calibration
plots were achieved in the ranges of 25-1200 ng/mL for DL and 50-1500 ng/mL for 5-HDL and 4-
HDLG (r2 ≥ 0.997) in rat plasma. The intra- and inter- assay precisions and accuracy were acceptable.
The overall recoveries of DL and its two main metabolites from rat plasma were between 97.12% and
103.12% with an RSD value between 0.34% and 4.57%.
Conclusion: The present study supports the possible use of the microemulsion mobile phase in LC as a
“greener ” mobile phase. The developed method offered an advantage in the form of direct analysis of
biological samples after appropriate dilution with eco-friendly microemulsion mobile phase, which
decreased the possibility of sample loss during analysis. The developed assay was successfully applied
in a pharmacokinetic study and it established the applicability of the method for the determination of
concentration-time profiles of DL and its two main metabolites in rat plasma after systemic administration.