Ten millilitres of blood will be drawn at 0 hours (baseline), 10 minutes, 30 minutes, 10 minutes before the end of the infusion, and 30 minutes, 1 hour, 2 hours after the end of the infusion. The blood will be drawn into 10 ml tubes (green topped) containing heparin and 5 micromol tetrahydrouridine. The tubes are then centrifuged at 3300 rpm for 15 minutes and the supernatant plasma is then transferred to plain tubes (red topped) for immediate storage at -80oC. Samples will be labeled with the patient's name, ID number, date, exact time of sample and protocol number. A pharmacokinetic form will accompany the plasma samples to the Pharmacology laboratory in the Department of Pharmacology, National University of Singapore, c/o Prof Lee How Sung.