257   Phosphorylation of Zidovudine (ZDV), Stavudine (d4T), and Abacavir (ABC) in Peripheral Blood Mononuclear Cells (PBMCs) in Treatment- Naive and Treatment- Experienced Patients.

T. L. Parsons*¹, C. Flexner¹, C. Hendrix¹, M. Paff², J. Bishop², D. Goodwin², N. Graham², J. Lee¹, J. Christopher¹, and F. Hamzeh¹.
¹Johns Hopkins Univ., Baltimore, MD and²Glaxo Wellcome, Res. Triangle Park, NC.

Background:Nucleoside analogue treatment failure, which is defined as a >0.5 log viral load increase, could be due to viral mutation or a reduction in drug phosphorylation in infected cells caused by prolonged exposure. In this study we investigated the effects of >12-months exposure to ZDV or d4T on the ex vivo phosphorylation of ZDV, d4T, and ABC.

Methods:PBMCs were isolated from 5 groups ( n = 10/group) of HIV infected patients (ZDV treated success or failure, d4T treated success or failure, and NRTI treatment naive). PBMCs were incubated ex vivo with tritiated ZDV, d4T, and ABC. Intracellular nucleoside analogue anabolites were determined by HPLC.

Results:Medians (pmol of drug/10⁶cells) and non-parametric-analyses (Mann-Whitney) of the data are shown below:

Conclusions:No statistically significant difference was seen in ZDV and d4T phosphorylation between ZDV- and d4T-experienced patients. Therefore, the sequence of these nucleoside analogues does not impact the degree of phosphorylation. Prior exposure (>12 months) to ZDV or d4T had no effect on ABC phosphorylation.