 - Study medications: Methadone and inulin administration Blood and urine will be collected for the purposes of this research project. Blood will be drawn from the indwelling arterial catheter that already is in place for clinical purposes. The amount of blood obtained for all study related determinations will be minimized and kept at less than 3 mLkg of blood per 48 hour period. The study will last 60 hours for group 1 and 72 hours for group. 