Extractive Spectrophotometric Determination of Tenofovir Disoproxil Fumarate Using Acidic Triphenylmethane Dyes

Tenofovir disoproxil fumarate is a nucleotide reverse transcriptase inhibitor that has activity against the hepatitis B and HIV viruses. Three simple and sensitive extractive spectrophotometric methods have been described for the assay of tenofovir disoproxil fumarate either in pure form or in pharmaceutical formulations. The developed methods involve formation of colored chloroform extractable ion-pair complexes of the drugs with triphenylmethane dyes, namely, bromothymol blue (BTB), bromophenol blue (BPB), and bromocresol purple (BCP) in acidic medium. The extracted complexes showed absorbance maxima between 410 and 415？nm. Beer’s law is obeyed in the concentration ranges 1.5–25, 1.0–25, and 1.25–25？μg？mL？1 with BTB, BPB, and BCP, respectively. The effectc of concentration of dye, pH, and interference of excipients have been studied and optimized. The limits of detection and quantification have been determined. All three methods are validated as per the guidelines of ICH. The methods have been applied to the determination of drug in commercial tablets and results of analysis were validated statistically through recovery studies. 1. Introduction Tenofovir disoproxil fumarate (TDF) 9-[(R)-2-[[bis[(isopropoxycarbonyl)oxy]methoxy]phosphinyl]methoxy]propyl] adenine fumarate is antiviral agent acts as nucleoside reverse transcriptase enzyme inhibitor [1]. It is a nucleoside analogue which is phosphorylated by host cell enzyme to give 5-triphosphate derivative. This moiety competes with the equivalent host cellular triphosphate for proviral DNA synthesis by viral reverse transcriptase which is viral RNA-dependent DNA polymerase. Incorporation of the 5-triphosphate moiety into the growing viral DNA chain results in chain termination. It is indicated in combination with other antiretroviral agents for the treatment of HIV-1 infection in adults [2, 3]. The literature survey revealed that only few methods are available for the determination of tenofovir in dosage forms and include liquid chromatography with tandem mass spectrometry [4, 5]; HPLC with solid phase extraction [6]; reversed phase HPLC [7, 8]; HPLC with spectrophotometric detection [9]; HPTLC [10]; gradient ion-pair LC with fluorescent detector [11]; and HPLC-UV, HPLC-MS [12], and first-order UV derivative spectrophotometry [13, 14]. Visible spectrophotometry, because of its simplicity, cost-effectiveness, sensitivity, selectivity, fair accuracy, and precision, has remained competitive in pharmaceutical analysis. In a method described by Onah and Ajima, tenofovir [15] was quantified by complexation