Patients will be contacted at the completion of week one prior to up titration, then at the end of week two to ensure tolerance and compliance with the 1000mg BID dose. Patients will perform the second CPET study at week four +/- 1 week. The trial medication will be assessed and counted to ensure that patients have taken there allotted pill count for the duration of the study. Patients who are found to be noncompliant of less than 80% will be excluded from the study.