Diclofenac is a potent inhibitor of
prostaglandin synthesis, as well as an established
antipyretic and
analgesic agent. To determine
diclofenac in rat bile and investigate its hepatobiliary excretion, a procedure using rapid and sensitive high-performance liquid chromatography coupled to microdialysis sampling system was developed. A shunt linear microdialysis probe was inserted into the common bile duct between the liver and the duodenum for continuous sampling of the
drug from bile fluids following
intravenous administration of
diclofenac (1 mg/kg). Separation and quantitation of
diclofenac in the bile
dialysates were achieved using a microbore reversed-phase C18 column (150x1.0 mm I.D.; particle size 5 microm) maintained at ambient temperature. Samples were eluted with a mobile phase containing 100 mM
sodium dihydrogenphosphate (pH 3.1)-acetonitrile (30:70, v/v), and the flow-rate of the mobile phase was 0.05 ml/min. The UV detector wavelength was set at 280 nm. The concentration-response relationship from the present method indicated linearity (r2>0.995) over a concentration range of 5-5000 ng/ml for
diclofenac. Intra-assay and inter-assay precision and accuracy of
diclofenac fell well within the predefined limits of acceptability (< or = 15%). The
diclofenac in rat bile appeared to have a slow elimination phase, with a peak concentration at 20 min following
diclofenac administration. The results demonstrated that
diclofenac might be secreted into bile in unconjugated form by a canalicular
bile acid transporter, and then go through hepatobiliary excretion. These results may provide good clinical evidence showing the value of
diclofenac for the treatment of biliary
colic. The elimination half-life of
diclofenac in the biliary elimination was prolonged by treatment with
cyclosporin A, indicating that the
drug-drug interaction might affect the hepatobiliary excretion of
diclofenac.