Must not use (or, depending on the agent, must not have used up to the last 28 days) of medications known to inhibit or induce cytochrome P450 during the initial period of the study period (Arm 1: Screening visit to Day 17; Arm 2: Screening visit to Day 15). After this initial period, use of these agents will be permitted on a case-by-case basis as per Investigator's clinical judgement; where necessary, additional PK studies may be performed. The prohibited medications include, but are not limited to: isoniazid, rifampin, rifabutin, astemizole, terfenadine, cisapride, cimetidine, triazolam, midazolam, quinidine, nifedipine, diltiazem, verapamil, amiodarone, or ergot alkaloids, carbamazepine, phenytoin and other hydantoins, phenobarbital and other barbiturates, propoxyphene, dexamethasone, oral contraceptives, antidepressants (fluoxetine, paroxetine, imipramine, amitriptyline, nefazodone), azole antifungals (ketoconazole, fluconazole, itraconazole) macrolide antibiotics (erythromycin, clarithromycin, dirithromycin), or grapefruit juice.