A Comparison of the Phenotypic Susceptibility Profiles of Emtricitabine and Lamivudine

Simultaneous quantification of emtricitabine and tenofovir nucleotides in peripheral blood mononuclear cells using weak anion-exchange liquid chromatography coupled with tandem mass spectrometry

“…TFV and its metabolites have, to the best of our knowledge, never been determined simultaneously in clinical samples, but in vitro and macaque experiments by others showed several different TFV:TFV-MP:TFV-DP ratios at similar concentrations [4,10,11,23]. TFV-MP levels that are higher than TFV-DP levels have, however, never been reported.…”

“…The methods used for sample collection and processing were, however, very similar to previously published methods. Cell isolation has been performed using CPTtubes [3,7,16] or ficoll paque [1,4,23], followed by washing steps using a cooled saline solution [3,15,16,23]. Since TFV can also be phosphorylated in red blood cells, some have performed a red blood cell lysis step [15,23].…”

“…The plasma half-lifes of FTC and TFV are, for example, 8-10 [1] and 14 [2] h, whereas intracellular half-lifes of 39 [1] and 150 [3] h have been observed for FTC-TP and TFV-DP, respectively. Moreover, metabolite levels are subject to inter-individual variation and intracellular drug-drug interactions [4]. Finally, low triphosphate levels can cause viral resistance, whereas high levels have been associated with treatment toxicity [5].…”

“…Direct LC-MS determination of FTC-TP and TFV-DP has been performed using the ion-pairing agents tetrabutylammonium [1,3,4,[8][9][10][11] and dimethylhexylamine [12][13][14][15][16] and weak anionexchange liquid chromatography (WAXLC-MS/MS) [17]. Although some of these methods also include TFV and/or TFV-MP [4,[10][11][12], none include FTC-MP or FTC-DP.…”

Simultaneous quantitation of the nucleotide analog adefovir, its phosphorylated anabolites and 2′-deoxyadenosine triphosphate by ion-pairing LC/MS/MS

“…The method was developed to facilitate the analysis of phosphorylated metabolites generated during in vitro cell culture incubations with hepatic cells as a more convenient, sensitive and selective alternative to the traditional technique of using radiolabeled parent nucleotide. We have previously reported findings obtained using earlier versions of this method including the characterization of the intracellular hepatic metabolism of adefovir [28], a comparison of adefovir metabolism to a structurally related nucleotide analog [29] and the results obtained using adapted methods to study other nucleoside and nucleotide analogs [29][30][31]. Here observations made during method development, significant refinement to the previously reported method and the results of cross-validations are described.…”