2. Regimen B; 150 mg single dose. All dosing will be supervised and documented. Subjects will have 2 hospitalizations to complete visit 2 and visit 3 in their assigned sequence within each. Each visit will require hospitalization for about 40 hours (2 nights and 2 days). The subject will be randomized to receive either regimen A or B on first admission (visit 2). Treatment allocation will be performed using computer-generated list of random permutations of AB sequence.