Study to Evaluate the Efficacy, Safety and Tolerability of PXT002331 (Foliglurax) in Reducing Motor Complications of Levodopa Therapy in Parkinson Disease's Patients

Inclusion Criteria: * Males or females diagnosed after the age of 30 years with idiopathic PD for at least 3 years * Disease severity of 2 to 4 on the modified Hoehn and Yahr scale when in the OFF state * Been treated with a stable regimen of levodopa-containing therapy * Subjects who are on a long-acting formulation of levodopa-containing therapy, including Apodespan PR (or equivalent), must be on a stable dose for at least 6 weeks prior to the first screening visit * Experienced motor fluctuations with wearing off over a period of at least 3 months prior to randomisation * Experienced LID over a period of at least 3 months prior to randomisation * Female subjects will be women of non-childbearing potential * Subjects must pass a Hauser diary concordance test * Subjects are able, with or without the help of a caregiver, to understand the purpose and risks of the study and provide signed and dated informed consent and authorisation to use confidential health information in accordance with national and local subject privacy regulations Exclusion Criteria: * Subjects with atypical, secondary or drug-induced Parkinsonism * Subjects with a Mini-Mental State Examination (MMSE) score \<25 * Any known contraindication to the use of levodopa, including a history of malignant melanoma or a history of narrow-angle glaucoma. * Subjects who have had a clinically significant illness within 4 weeks of first dose, as determined by the Investigator. * Any advanced, severe or unstable disease (other than PD) that may interfere with the primary and secondary study outcome evaluations * Subjects who have undergone prior neurosurgical operation for PD or transcranial magnetic stimulation. * Subjects who are participating in another clinical study (eg, attending follow-up visits) or who have participated in a clinical study involving administration of an investigational drug (new chemical entity) in the past 3 months prior to the baseline visit. * Female subjects of childbearing potential * Subjects who are pregnant (as determined by positive serum pregnancy test at screening and/or baseline), breastfeeding or lactating. * Subjects who, in the opinion of the Investigator, should not participate in this study.