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Background:  Significant levels of intracellular d4T-TP in HIV-infected subjects treated with zidovudine have been reported. Our objective was to determine the alleged in vivo intracellular transformation of ZDV to d4T in HIV-infected subjects producing measurable d4T-TP concentrations.

Methods:  We developed and validated an HPLC-MS/MS method for the simultaneous determination of d4T-TP, 3TC-TP, and ZDV-TP. We monitored the d4T-TP signal in more than 100 samples from HIV-infected subjects that were on stable d4T therapy. In addition, we monitored the signal for d4T-TP and ZDV-TP in more than 450 samples from HIV-infected individuals that were on ZDV for at least 12 weeks. Finally, we performed in vitro CEM_SS studies incubating with 10 and 100 µM of ZDV.

Results:  We could measure d4T-TP concentrations from HIV-infected individuals who were on staduvine with a limit of quantitation (LOQ) of 43 fmol. However, we did not obtain any substantial signal (above LOQ) for d4T-TP concentrations from any of the 450 samples that were collected from patients taking zidovudine. Furthermore, in vitro studies did not produce any signal for d4T-TP despite the substantial amount of measurable ZDV-TP from the cells. We believe that the transformation of ZDV to d4T in the aforementioned article is chemically dependent and not biological mediated. We are determining the chemical step responsible for such transformation.

Conclusions:  No evidence was found for the in vivo transformation of ZDV to d4T in HIV-infected subjects.

Keywords: d4t-TP; ZDV-TP; intracellular concentrations