November-December 2016 Indian Journal of Pharmaceutical Sciences 775 Research Paper Development and Validation of a Novel Colorimetric Method for the Estimation of Emtricitabine in Bulk and Tablet Formulation T. N. V. GANESH KUMAR, S. VIDYADHARA, T. D. KUMAR, D. JASWANTH, K. VIJETHA AND B. G. PRIYADARSHINI Department of Pharmaceutical Analysis, Chebrolu Hanumaiah Institute of Pharmaceutical Sciences, Guntur 522 019, India Ganesh, et al.: Development and Validation of a Colorimetric Method for the Estimation of Emtricitabine A simple and new colorimetric method was developed for the estimation of emtricitabine. The proposed colorimetric method is based on the diazotisation of amine group present in emtricitabine, followed by colour complex formation using β-naphthol reagent. Parameters affecting the reaction were studied and conditions were optimized. The absorption maximum for the colour complex was observed at 559 nm. Linearity was obtained in the concentration range of 100-500 µg/ml for emtricitabine colour complex. The developed method was optimised and validated. The method was successfully applied for the estimation of emtricitabine in bulk and in tablets. This is the frst method reported for colorimetric estimation of emtricitabine. Key words: Emtricitabine, diazotisation, β-naphthol, colorimetry Emtricitabine is a nucleoside reverse transcriptase inhibitor (NRTI) for the treatment of HIV infection in adults and children. This drug is most widely used in antiviral therapy. It is indicated in combination with other antiretroviral agents to treat HIV infection [1,2] . Chemically, emtricitabine is 4-amino-5-fuoro-1- [(2R,5S)-2-(hydroxymethyl) -1,3-oxathiolan-5-yl]- 1,2-dihydropyrimidin-2-one (fg. 1). It is one among the list of most essential medicines in health system, according to the World Health Organisation [3] . Several analytical methods using Reversed-phase high- performance liquid chromatography (RP-HPLC), UV and Liquid chromatography-mass spectrometry (LC- MS) were reported for the estimation of emtricitabine in bulk, formulations and biological samples like human plasma/serum [4-6] . Fluorimetric method for the estimation of emtricitabine in plasma samples was also reported [7] . Most of the developed methods were robust and accurate. Although these methods have proven to be good for the estimation of emtricitabine, till date there is no colorimetric method for its estimation has been reported. A colorimetric estimation method for emtricitabine can be developed due to its free amino functional group present at 4 th position of pyrimidine ring. In the present work, we have focussed on development of colour complexes, which are stable and their absorbance is linear with concentration. Diazonium salts are involved in the substitution, coupling and replacement reactions. Azo dyes have been prepared using this process [8] . The temperature should be maintained and the solutions should be freshly prepared because the diazonium salts are very unstable and tend to be explosive as solids [9-11] . The present colorimetric method would be effcient and simple for the estimation of emtricitabine alone in bulk and pharmaceutical formulation. MATERIALS AND METHODS All chemicals used in the present study were of *Address for correspondence E-mail: ganeshtnv@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 22 November 2016 Revised 18 October 2016 Received 12 December 2015 Indian J Pharm Sci 2016;78(6):775-779 Fig. 1: Structure of emtricitabine. N N H 2 N F O S O OH