Quantitative determination of duloxetine and its metabolite in rat plasma by HPLC-MS/MS.

The major metabolite of duloxetine is a glucuronide conjugate of 4-hydroxy duloxetine (4-HD). However, interestingly, there have been no reports determining concentrations of 4-HD and no fully validated method has been established for measuring duloxetine and 4-HD in rat plasma. We developed a method for the simultaneous quantification of duloxetine and its metabolite in rat plasma using high-performance liquid chromatography tandem mass spectrometry. Duloxetine and 4-HD were analyzed on a reverse-phase C18 analytical column after protein precipitation of the plasma sample with methanol, using carbamazepine as an internal standard. The isocratic mobile phase of 5 mm ammonium acetate-methanol (4:6, v/v) was eluted at 0.4 mL/min. Quantification was performed on a triple-quadrupole mass spectrometer using electrospray ionization, and the ion transition monitored in selective reaction monitoring mode. The coefficient of variation for assay precision was <18.0%, and the accuracy was 84.0-118.0%. This method was successfully used to measure the concentrations of duloxetine and its metabolite in plasma following the oral administration of a single 40 mg/kg dose in rats.

Anti-diarrheal and spasmolytic activities and acute toxicity study of Soonkijangquebo, a herbal anti-diarrheal formula.

The anti-diarrheal and spasmolytic activities of Soonkijangquebo (SKJQB), a Korean herbal anti-diarrheal formulation, were subjected to pharmacological evaluation. SKJQB, at a dose of 50-200 mg/kg, inhibited castor oil-induced diarrhea in mice. The median effective dose (ED50) for the anti-diarrheal effect was 93 mg/kg. In isolated rabbit jejunum preparations, SKJQB produced a spasmolytic effect by the relaxation of spontaneous contractions in a dose-dependent manner. The median effective concentration (EC50) for the spasmolytic effect was 3.6 mg/ml. In isolated guinea pig ileum preparations, SKJQB also produced a spasmolytic effect by reduction of acetylcholine-induced contractions. When tested against calcium channel blockade in rabbit jejunum, SKJQB caused a dose-dependent rightward shift in the Ca2+ dose-response curves, similar to that produced by verapamil, a well-known calcium antagonist. In an acute toxicity study in Sprague-Dawley rats, the median lethal dose (LD50) of SKJQB was greater than 2000 mg/kg, and no pathological changes were noticed in macroscopic examination by necropsy of rats treated with SKJQB. Thus, SKJQB may be safely used as a spasmolytic as well as an anti-diarrheal agent.