Predicted plasma d4T (grey) and cellular d4T-TP (TP, black) concentrations are shown for individuals taking d4T (without indinavir) at dosages of: 40 mg twice a day (bid) (A) or 30 mg bid (B). Analogous predicted concentration are also shown for individuals taking d4T (with indinavir) at 40 mg bid (C), and 30 mg bid (D). Medians (solid curves), 5th 25th and 75th and 95th percentiles (dashed curves), were calculated using data from 2,000 simulated individuals from each cohort, and are plotted together with the Ki of d4T-TP versus wild type HIV-1 RT measured in vitro in the presence of competing thymidine-5′-triphosphate (TTP).