A new method for determination of efavirenz and pKa by using LC-UV
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Efavirenz (EFA) is a non-nucleoside reverse transcript-inhibitor (NNRTI) and clinically, it is used as a part of a highly active antiretroviral therapy for the treatment of a human immunodeficiency virus. This research has been concerned with the determination of pKa values and the development of simple, specific, accurate and reproducible isocratic reversed phase high performance liquid chromatographic (RP-HPLC) method which has been subsequently validated using ICH recommendations for the determination of Efavirenz (EFA) in tablet dosage forms. Indapamide (IDP) was used as an internal standard and it was the first of the new class of antihypertensive diuretic. The determination was carried out for a runtime of 8 min at 30˚C on a X-terra RP-18 column having 250mm x 4.6mm i.d. with 5μm particle size and 20 mM sodium dihydrogen phosphate buffer adjusted to pH 5.0, and acetonitrile (70:30 v/v) was used as a mobile phase at a constant flow rate of 1.0 ml/min with UV detection wavelength of 247 nm for EFA and 240 nm for IDP. The retention time of IDP and EFA was about 3.6 and 6.9 min with the correlation coefficient of 0.999 and 0.999; respectively. The linearity was established at 1-12 µg/ml for EFA, and the LOD and LOQ values were found to be 0.083 and 0.261 with the recovery of 100.06%. The pKa values of EFA have been determined precisely in different acetonitrile–water binary mixtures (60-65 % v/v) using retention factors. The method developed in this study can be used in routine analysis of EFA in pharmaceutical quality control laboratories and pharmacokinetic studies.