New atazanavir information
Jules Levin for NATAP.org
Kate Squires, of the University of Southern California, reported new information regarding atazanavir (ATV) at the Bristol-Myers Squibb Symposium at the IAS Conference.
Squires addressed the results of BMS ATV Study 034, which compared ATV to efavirenz (EFV), each combined with AZT/3TC. In this study through week 48 BMS reported 32% of patients receiving ATV had <50 copies/ml (ITT) and 37% taking EFV had < 50 copies.
Although the percentage of patients who had <50 c/ml were about the same for both treatment groups, observers were confused as to why the viral response to EFV was so low and why it was lower than seen in other EFV studies. Regarding <400 c/ml, the previously reported data from Study 034 was that 70% of patients taking ATV had <400 c/ml and 64% of patients taking EFV had <400 c/ml at week 48 (ITT).
At the BMS Symposium, Squires reported data related to this (see Table 1 and 2).
She said that viral load samples in the BMS 034 Study were collected in PPT tubes and were spun and frozen in situ prior to shipping to a centralised lab. Additional samples were collected at study visits week 12, 24, and 48 in EDTA tubes (spun, separated, frozen, and were shipped from the study site).
Squires presented new information on the effect of using PPT vs EDTA tubes on viral load measurements. Duplicated samples were assayed after collection in PPT or EDTA tubes.
Five hundred and eight-four patients were evaluable (300 on ATV, 284 on EFV): there were 805 patients in the main study at enrollment; 584 represents 88% of the 661 subjects treated for 48 weeks; 584 represents 73% of all 805 patients treated in the main study. Squires said the sample handling methodology affected the viral load responses.
Table 1: Effect of using PPT vs EDTA tubes on viral load measurements at Week 48 (LOQ = limit of quantification)
|LOQ <400 c/ml||LOQ <50 c/ml|
Table 2: Percent undetectable by continent
LOQ <400 c/ml for ATV:
|No America||94%||89%||+ 7%|
LOQ <50 c/ml:
Although these data were presented at a pharmaceutical satellite meeting and not within the ‘peer reviewed’ context of the main meeting, it is important to be aware of these new results. It goes some way to allay the concerns over potency of atazanavir (and efavirenz) seen in this atazanavir registrational study.