The study will consist of five separate visits to the Clinical research Center at the University of Florida and each visit will last anywhere from 6-8 hours. Patients will be given a diary of questionnaires where they will record when they take their medication and any side effects they might have. Patients will also have Electrocardiograms (ECGs) to make sure they are healthy enough to be a participant in the study and to measure the effects of their medication on their heart. During this study, patients will continue treatment of their Mycobacterium avium Complex infections. Patients will be observed taking their medication on each of the five separate days. On each of these days patients will have blood drawn at 2 and 6 hours after their drugs are taken in order to measure drug levels in their blood. We will also use this blood to measure levels of proteins and hormones and to make sure the medications are not affecting the patient's heart. The patient will fill out several questionnaires and do a dietary assessment online. Investigators will assess the patient's body make-up using a device called the Bod Pod. The patient will also be assigned to one of two treatment groups: (1) Ondansetron 8mg (Zofran®, GlaxoSmithKline, Research Triangle Park, NC) every morning before breakfast versus (2) a dietary supplement prior to taking daily medication. The patient will be assigned to the first treatment group for a period of two weeks. On the third study visit investigators will switch the patient to the second group.