Journal of Chromatography B, 835 (2006) 131–135 Short communication Simple and rapid liquid chromatography method for determination of efavirenz in plasma Geetha Ramachandran a , A.K. Hemanth Kumar a , Soumya Swaminathan a,∗ , P. Venkatesan a , V. Kumaraswami a , David J. Greenblatt b a Tuberculosis Research Centre (Indian Council of Medical Research), Chetput, Chennai, India b Department of Pharmacology & Experimental Therapeutics, Tufts University School of Medicine, Boston, USA Received 6 December 2005; accepted 5 March 2006 Available online 29 March 2006 Abstract A simple and rapid high performance liquid chromatographic method for determination of efavirenz in human plasma was developed. The method involved extraction of sample with ethyl acetate and analysis using a reversed-phase C 18 column (150 mm) with UV detection. The assay was linear from 0.0625 to 10.0 g/ml. The method was specific for efavirenz estimation and the drug was stable in plasma up to one month at -20 ◦ C. The average recovery of efavirenz from plasma was 101%. Due to its simplicity, the assay can be used for pharmacokinetic studies and therapeutic drug monitoring of efavirenz. © 2006 Elsevier B.V. All rights reserved. Keywords: Efavirenz; Plasma; HPLC 1. Introduction Efavirenz, a non-nucleoside reverse transcriptase inhibitor (NNRTI), is being increasingly used since 1998 in association with other antiretroviral agents in the treatment of HIV infection [1]. Its long half-life allows once-daily dosing, and therefore presents an advantage for treatment compliance and efficacy [2–4]. Efavirenz undergoes extensive metabolism, mainly by the cytochrome P-450 isoenzyme, CYP2B6, which is known to exhibit extensive inter-individual variability. This could lead to heterogeneity in response to treatment. In addition, differences in efavirenz pharmacokinetics between various racial/ethnic groups have been reported [5–8]. Efavirenz is the preferential choice to treat HIV-tuberculosis (TB) co-infected patients. Management of both these diseases is complicated due to pharmacological drug–drug interactions between efavirenz and rifampicin, which is a first-line anti-TB drug and a potent inducer of the cytochrome P-450 system. ∗ Corresponding author at: Division of HIV/AIDS, Tuberculosis Research Centre, Chetput, Chennai-600031, India. Tel.: +91 44 2836 9698; fax: +91 44 2836 2528. E-mail address: doctorsoumya@yahoo.com (S. Swaminathan). Rifampicin is reported to reduce efavirenz plasma levels by 13 to 25%, which could have therapeutic implications [9]. The low genetic barrier of efavirenz could induce a high level of phe- notypic resistance [10]. The emergence of efavirenz-resistant mutants is likely to be facilitated by repeated exposure to sub- therapeutic drug levels. It has been suggested that efavirenz plasma levels can serve as predictors of treatment failure in HIV- infected patients [11–14]. Treatment failure and central nervous system side effects were found to be associated with low and high efavirenz plasma levels [15]. Therefore monitoring of efavirenz levels in plasma could be useful in the clinical management of HIV disease, especially in HIV-TB co-infected patients, who are being treated with efavirenz and rifampicin concomitantly. A number of high performance liquid chromatography (HPLC) methods for estimation of plasma efavirenz alone [16–20] and in combination with other antiretroviral agents [21–31] have been reported. While some of these meth- ods involve cumbersome and lengthy extraction procedures [19,20,23,25], few other methods have utilized a complex mobile phase [21,25] or gradient mobile phase [22,29]. Sample pretreatment by liquid-liquid extraction with diethyl ether [16,18,22,30,31] or protein precipitation with acetonitrile [17,27] has also been carried out in some methods. Most of these methods have used a 250 mm column, where the run time 1570-0232/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jchromb.2006.03.014