The companies established a U.S. joint venture last December to develop a Truvada-Sustiva pill. Gilead said the first formulation failed because the Sustiva levels measured in patients' blood were too low. Because blood levels of Sustiva in the combination pill were less than those of Sustiva alone, the experimental pill failed to achieve bioequivalence. The companies must meet this standard to convince the FDA to approve the new pill. The companies say a once-a-day combination pill "may help simplify HIV therapy." Gilead's Truvada is, itself, a once-a-day combination drug containing Emtriva and Viread.