Linear relationship was obtained between the peak area and the corresponding concentrations. The equations of linear regression were performed using least-square method. Retention time was Gefitinib concentration obtained at 9 min. Chromatogram was shown in Fig. 1. The plasma concentration vs. time profiles of Metoprolol in rats following oral treatment of Metoprolol with and without Duloxetine were

shown in Fig. 2. From the comparison of plasma concentration profiles of Metoprolol in the absence and presence of Duloxetine, it is clear that there is significant elevation of plasma concentration of Metoprolol in the combination group at following time points 1st hour (p < 0.001), 1.5 h 1st hour (p < 0.001), Selleckchem UMI-77 2nd hour (p < 0.001), 2.5 h 1st hour (p < 0.01). Line graph ( Fig. 2) clearly speaks that the Metoprolol concentrations in the combination group were even slightly present at 24th hour where as in Metoprolol alone group, drug has almost eliminated at 9th hour. These clearly indicate the increased elimination half-life of the drug and mean retention time of the drug in the body. The pharmacokinetic

parameters of Metoprolol were calculated using Try-Kinetica software and the parameters includes half-life (t1/2), clearance (CL), volume of distribution (Vd), maximum concentration (Cmax), time to reach maximum concentration (Tmax) and area under the curve (AUC). The calculated pharmacokinetic parameters of Metoprolol in rats were shown in Table 1. Results of this pharmacokinetic study reveal that Duloxetine (20 mg/kg, p.o.) increases the plasma exposure levels of Metoprolol (25 mg/kg, p.o.) in single dose acute study which was clearly evident from the significant elevation of AUC0–24 (p < 0.01), most AUC0–inf (p < 0.01). At the same time, Duloxetine has not significantly increased the Cmax. T1/2 (p < 0.05) of Metoprolol is

prolonged along with Duloxetine administration. Duloxetine treatment along with Metoprolol results in 3.38 fold significant (p < 0.01) increase in the AUC0–24 of Metoprolol, three fold significant (p < 0.01) increase in the AUC0–α of Metoprolol, 3.4 fold increase in T1/2 of Metoprolol without significant alteration in Cmax of Metoprolol. The observed interaction between Duloxetine and Metoprolol in this study is further supported by previous results which reveal that potent CYP2D6 inhibitor paroxetine has been shown to increase the biologically available dose of Metoprolol about 4–6 fold. The same degree of increase was observed for the two other potent CYP2D6 inhibitors in the class, fluoxetine and bupropion. Severe bradycardia and atrioventricular block has been reported in patients who have taken Metoprolol in combination with these three drugs. Escitalopram, citalopram and Duloxetine are less potent CYP2D6 inhibitors, and have been shown to cause 2- to 3 fold increases in biologically available dose of Metoprolol.