Orally Administered ENT-01 for Parkinson's Disease-Related Constipation (KARMET)

This study will be conducted as a multi-center, randomized, double-blind, placebo-controlled study. Approximately 72 patients will be randomized 3:1 to treatment or placebo, with approximately 54 patients allocated to receive the active investigational product and approximately 18 patients allocated to receive placebo. \- Study Update- Amendment 3 - In this amendment, an additional 80 patients (approximately) will be randomized 1:1 to treatment or placebo (double-blind) with approximately 40 subjects allocated to each group.

The study will be conducted on an out-patient basis. Each patient will have 6 visits to the clinic: a screening visit, a randomization visit, 3 follow up visits, and 1 end of study visit. Patient randomization will be stratified based upon the baseline weekly complete spontaneous bowel movement rate (CSBM) established during the screening period. Patients will be allowed to adjust their dosing, based upon protocol specifications. Rescue medications will be provided to all patients to ensure they move their bowels on a regular basis. Patients will also be asked to participate in up to 2 sub-studies: a pk study and/or a stool microbiome study. The first 20 patients to consent to the pk study will have additional blood samples taken at randomization and at 2 follow up visits. The first 20 patients to consent to the stool microbiome study will provide stool samples at randomization and at 2 follow up visits.