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Simultaneous determination of sildenafil and tadalafil in herbal medicines by HPLC

The HPLC method for the simultaneous determination of 2 PDE-5 (sildenafil and tadalafil) in herbal medicines was validated. Using acetonitrile and water as the mobile phase, Gemini C18 (250 x 4.6 nm, 5 µm) column, UV detection at 285 nm and flow at 1 ml/min, the PDE-5 were separated satisfactorily within 6 minutes, | Journal of military pharmaco-medicine 7-2013 SIMULTANEOUS DETERMINATION OF SILDENAFIL AND TADALAFIL IN HERBAL MEDICINES BY HPLC Nguyen Thi Hao*; Nguyen Van Bach*; Nguyen Van Thinh* Dao Van Don*; Pham Van Hinh*; Nguyen Thi Thanh Phuong** Summary The HPLC method for the simultaneous determination of 2 PDE-5 (sildenafil and tadalafil) in herbal medicines was validated. Using acetonitrile and water as the mobile phase, Gemini C18 (250 x 4.6 nm, 5 µm) column, UV detection at 285 nm and flow at 1 ml/min, the PDE-5 were separated satisfactorily within 6 minutes. The quantitation limits of sildenafil citrate and tadalafil were about 0.2 g/ml and 0.3 g/ml, respectively. The calibration curve of each PDE-5 had a correlation coefficient close to 1. The precisions were all less than 2%. The recovery rates of extraction were 92 - 100% for all PDE-5. This method can be used to detemine sildenafil citrate and tadalafil simultaneously in herbal medicines. * Key words: PDE-5; Sildenafil citrat; Tadalafil; HPLC; Herbal medicines. INTRODUCTION Sildenafil citrate, 1-[4-ethoxy-3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo [4,3d]pyrimidin-5-yl)phenylsulfonyl]-4 methylpiperazine, is primarily indicated in the treatment of erectile dysfunction. It is rapidly absorbed after oral administration, with absolute bioavailability of about 40%. It is rapidly and extensively metabolized in the liver to the active N-desmethyl sildenafil metabolite. Under steady state conditions, the plasma concentrations of N-desmethyl sildenafil were approximately 40% of those measured for sildenafil. Tadalafil, (6R,12aR)-2,3,6,7,12,12a-hexahydro-2-methyl-6-[3,4-(methylenedioxy) phenyl] pyrazino[1’,2’:1,6]pyrido[3,4-b]indole-1,4-dione [1] is a newly approved oral selective phosphodiesterase-5 (PDE5) inhibitor indicated for the treatment of erectile dysfunction [1, 2, 3, 4]. The mechanism of action of tadalafil is similar to the other PDE5 inhibitors, sildenafil. Through the inhibition on PDE5, tadalafil .