147 Intracellular Phosphorylation of Zidovudine and Lamivudine in Peripheral Blood Mononuclear Cells in HIV-infected Adolescents and Young Adults on Once- vs Twice-daily Regimens J. H. Rodman*1, B. L. Robbins1, J. Martinez2, J. C. Lindsey3, A. Fridland1, J. F. Rodriguez4, P. M. Flynn1 1St Jude Children's Res Hosp, Memphis, TN; 2Northwestern Univ, Chicago IL; 3Harvard Sch of Public Hlth, Boston, MA; and 4Univ of Puerto Rico Sch Med, San Juan
Background: Intracellular Zidovudine (Z) and Lamivudine (L) metabolism to triphosphate (TP) in Peripheral Blood Mononuclear Cells (PBMCs) is necessary for antiviral activity, and intracellular Z-TP and L-TP persist for a substantially longer time than Z and L in plasma. The aims of this study were to 1) compare Z-TP and L-TP in PBMCs in patients (pts) receiving the same total daily dose when given BID and QD, and 2) determine the 24-hr time course of all phosphorylated metabolites of Z and L during chronic therapy on a QD regimen.
Methods: HIV-infected pts (12-24 yrs) with CD4 > 250 cells/ml receiving ZDV (600 mg/day) and 3TC (300 mg/day) received QD and BID regimens for 7-14 days with demonstrated compliance in a crossover design randomized for regimen sequence. Predose blood samples were obtained after a minimum of 7 days on QD and BID regimens. Serial blood samples (n = 6) were obtained over 24 hours in each subject on the QD regimen. PBMCs were isolated and intracellular mono- (MP), di- (DP), and tri- (TP) phosphates for Z and L were measured. The ratio for Z-TP and L-TP for BID to QD was calculated as a measure of persistence for each regimen. Summary statistics are median (Med) and range (r).
Results: Data were evaluable for 24 of 32 subjects enrolled. Data excluded were for insufficient sample (4) or protocol deviation (4). Med (r) for predose L-TP (picomoles per 106 cells) given BID was 2.8 (0.1-11.1) and for QD was 1.6 (0.1-6.3) and for predose Z-TP (femtomoles per 106 cells) was 16.4 (4.8-88.1) for BID and 11.3 (3.9-36.4) for QD. The BID/QD ratio was 1.4 for L and 1.3 for Z. Z-TP was not detectable for QD in 3 subjects, and the ratio was not determined. Med (r) L-TP maximum was 5.1 (0.3-10.9) at 6 (4-12) hrs. Med (r) Z-TP maximum was 54 (5.4-270) at 4 (2-12) hrs. L-TP and Z-TP at 0 and 24 hrs were consistent within pts. However, the co-efficients of variation for L-TP and Z-TP at 24 hrs among pts were 77% and 63% indicating substantial inter-subject variability.
Conclusions: The pattern of L phosphorylation in PBMCs provides a supporting rationale for QD dosing. The time course of Z phosphorylation is more rapid, but measurable Z-TP persisted over 24 hrs for the QD regimen in 21 of 24 subjects. Subjects with low Z-TP at 24 hrs on a QD regimen also have what may be sub-therapeutic values (< 7) with the BID regimen. These results provide support for further examining single daily regimens of Z with L and provide a detailed description of Z and L phosphorylation in pts.
