The FD treatment groups will consist of a low dose group receiving 60µg b.i.d. and a high dose group receiving 240µg b.i.d. Patients in the high dose group will dose escalate weekly by 60µg b.i.d. until they reach the fixed dose of 240µg b.i.d. Once patients in these treatment groups have reached their assigned maximum dose of active drug, weekly increases in the number of placebo tablets administered will continue in order to maintain the blind.