VRUS (R7128 pre-clinical kidney tox)
The first was a 6-month safety study in monkeys at doses of 200 to 2000 mg/kg/day, in July 2007, which was stopped after 13 weeks, as there were clear signs of clinical toxicity across all dose cohorts and an NOAEL was not established. A second monkey tox study started in April 2008 with a lower dose range - 10, 40, 100, and 600 mg/kg/day. No outward clinical effects were observed and if memory serves, VRUS thought the NOAEL in monkeys is well under 600 mg/kg/day.
One more on the reassuring side:
It is not seen in rats, despite substantially higher doses.
Still, the design of the phase 2b - enrollment in 2 cohorts, with the larger portion of the study contingent on the safety results from the first smaller one, shows the kidney tox concerns.