Background: AIDS defining events occur infrequently in the presence of CD4 counts above 200 cells/microL. It is, however, uncertain for most of the AIDS defining conditions whether this threshold can be considered equally safe in patients with a previously very low CD4 nadir.
Methods: We evaluated in detail all the AIDS defining events observed during a 48-week clinical trial in 1251 nucleoside reverse transcriptase inhibitor-experienced patients who started protease inhibitors (PIs) at CD4 counts below 50 cells/microL. The type of event, immunological status at the moment of event and time between start of PI treatment and event occurrence were analysed cumulatively and by event type; event rates were calculated.
Results: Concomitant data on CD4 counts were available for 338 AIDS defining events (81% of total events). Median time between start of treatment with PI and event was 94.5 days and median absolute CD4 value at the occurrence of event was 20 per microL. Only 14 events (in 12 patients) were observed above the threshold of 200 CD4 cells/microL. An analysis of the 67 deaths with concomitantly available CD4 counts (57%) showed a median CD4 count of 10 cells/microL, with only four deaths occurring in the presence of a CD4 count above 100 cells/microL.
Conclusions: Very few clinical AIDS defining conditions were observed in patients who start PIs at very low CD4 counts and with treatment restore absolute values in CD4 counts above 200 cells/microL. This threshold can therefore be considered a clinically effective goal of treatment with respect to occurrence of all AIDS defining conditions in patients starting PIs in very advanced HIV disease.