After at least 4 days on this dose, patients will be admitted to the hospital for 1 day for blood sampling before the drug dose and then at 0.5, 1, 1.5, 2, 4, 6, 8, 12, and 24 hours after the dose. Kidney function will be assessed by blood tests within 2 days of the blood sampling. If kidney function is not within the normal range, further dosing and blood sampling will be delayed until kidney function returns to the normal range.