November-December 2017 Indian Journal of Pharmaceutical Sciences 885 Research Paper Praziquantel (PRQ) is a derivative of pyrazinoiso quinoline with IUPAC name [2-(cyclohexyl- carbonyl)-1,2,3,6,7,11b-hexahydro-4H-pyrazino [2,1- a]isoquinoline-4-one]. Due to its high effcacy and low toxicity, it is widely used for the treatment of many diseases, such as human trematode, cestode infections, schistosomiasis, and many other infections pathogenic conditions to human [1] . From the very beginning different analytical methods were developed by different researchers and reported its level in animals and humans from a biological fuids (plasma, serum), tissue organ extracts. Some of the analytical methods, which include radiometric assay [2] , fuorometric assay [3] , enzyme-linked immunosorbent assay (ELISA) [4] , thin- layer chromatography (TLC), gas chromatography (GC) [5,6] , high-pressure liquid chromatography (HPLC) [7,8-14] . Literature demonstrates that a number of researchers have reported the sample preparation procedures and methods but due to its lengthy time-consuming single step or three-step liquid-liquid extraction [15] process, it is not reproducible technically. To avoid this drawbacks and making this process reproducible to produce clean samples clear chromatograms this method was developed for the estimation of PRQ in rat plasma using diazepam as an internal standard. This method is simple, sensitive and a selective for determination of PRQ in plasma. In this research work, we reported a very simple and single step sample preparation method based on the protein precipitation by using perchloric acid as a protein precipitating agent. The protein precipitation method was very effcient in giving a clear chromatogram that does not require solvent evaporation by a gentle stream of nitrogen or oxygen. Moreover, this method uses less plasma in this study. High-Performance Liquid Chromatography Determination of Praziquantel in Rat Plasma; Application to Pharmacokinetic Studies S. DEY, M. GHOSH, N. K. RANGRA*, K. KANT, S. R. SHAH 1 , P. K. PRADHAN 1 AND S. SINGH Department of Pharmaceutical Sciences and Technology, Birla Institute of Technology, Mesra, Ranchi-835 215, 1 Sigma Institute of Pharmacy, At-Bakrol, Waghodhai, Near Ajwa Nimata Road, Vadodara-390 019, India Dey, et al.: HPLC Method for Determination of Praziquantel in Rat Plasma A very simplistic, selective, sensitive, and reproducible procedure based on a reversed-phase high- performance liquid chromatography was used and developed for the determination of praziquantel in rat plasma. For the separation of praziquantel from the internal standard, diazepam on an Enable, C18 column (250×4.6 mm, 5 µm particle size), with the retention time of 6.4, 8.5 min, respectively. For praziquantel with UV detector at 225 nm. The mobile phase was a mixture of acetonitrile:water in a ratio of (60:40 v/v), running through the column at the fow rate of 1 ml/min. Sample preparation of 200 µl of plasma was done by a protein precipitation by using perchloric acid. Calibration curve was found to be linear with correlation coeffcients (r 2 ) is 0.9989 prepared in plasma at the concentrations of 5 to 1000 ng/ml. The precision of the above method was based on inter-day, and intra-day repeatability, and reproducibility (day-to-day variation) were found to be within the limit of 15%. Limit of quantifcation was accepted and found to be 5 ng/ml using 200 µl samples. The method appears to be robust and has been applied to a pharmacokinetic study of praziquantel in three groups of rats with a single oral dose of 40 mg/kg body weight. Key words: Praziquantel, reversed-phase high-performance liquid chromatography, limit of quantifcation, rat plasma *Address for correspondence E-mail: nareshrangra@gmail.com This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms Accepted 05 September 2017 Revised 08 March 2017 Received 08 August 2016 Indian J Pharm Sci 2017;79(6):885-892