Gilead shares sank nearly 5% to $40.70 after hours. According to the company, a pill combining Gilead's Truvada and Bristol-Myers Squibb's (BMY - Get Report) Sustiva didn't provide the same medication levels in a patient's blood as separate doses of each drug would.
In April, Gilead said it
Pending the results of the studies, Gilead and Bristol-Myers Squibb expect to file a new drug application with the Food and Drug Administration in the first half of 2006. If approved, the new pill would be the first complete treatment regimen of its kind available in a fixed-dose combination taken once a day.Bristol-Myers shares were down a penny to $25.10.