Effect of BIA 6-512 at Steady-state on the Levodopa Pharmacokinetics With a Single-dose of Levodopa/Benserazide 200/50 mg or With a Single-dose of Levodopa/Benserazide 200/50 mg Plus a Single-dose of Nebicapone 150 mg

Inclusion Criteria: * Male or female subjects aged between 18 and 45 years, inclusive. * Subjects of body mass index (BMI) between 19 and 30 kg/m2, inclusive. * Subjects who were healthy as determined by pre-study medical history, physical examination, vital signs, complete neurological examination and 12-lead ECG. * Subjects who had negative tests for HBsAg, anti-HCVAb and HIV-1 and HIV-2 Ab at screening * Subjects who had clinical laboratory test results clinically acceptable at screening and admission. * Subjects who had a negative screen for alcohol and drugs of abuse at screening and admission. * Subjects who were non-smokers or who smoked ≤ 10 cigarettes or equivalent per day. * Subjects who were able and willing to gave written informed consent. * (If female) She was not of childbearing potential by reason of surgery or, if of childbearing potential, she used one of the following methods of contraception: double barrier, intrauterine device or abstinence. * (If female) She had a negative urine pregnancy test at screening and admission. Exclusion Criteria: * Subjects who had a clinically relevant history or presence of respiratory, gastrointestinal, renal, hepatic, haematological, lymphatic, neurological, cardiovascular, psychiatric, musculoskeletal, genitourinary, immunological, dermatological, endocrine, connective tissue diseases or disorders. * Subjects who had a clinically relevant surgical history. * Subjects who had a clinically relevant family history. * Subjects who had a history of relevant atopy. * Subjects who had a history of relevant drug hypersensitivity. * Subjects who had a history of alcoholism or drug abuse. * Subjects who consumed more than 14 units of alcohol a week. * Subjects who had a significant infection or known inflammatory process on screening or admission. * Subjects who had acute gastrointestinal symptoms (e.g., nausea, vomiting, diarrhoea, heartburn) at the time of screening or admission. * Subjects who had used medicines within 2 weeks of admission that may affect the safety or other study assessments, in the investigator's opinion. * Subjects who had previously participated in a clinical trial with BIA 6-512. * Subjects who had used any investigational drug or participated in any clinical trial within 6 months prior to screening. * Subjects who had participated in more than 2 clinical trials within the 12 months prior to screening. * Subjects who had donated or received any blood or blood products within the 3 months prior to screening. * Subjects who were vegetarians, vegans or have medical dietary restrictions. * Subjects who cannot communicate reliably with the investigator. * Subjects who were unlikely to co-operate with the requirements of the study. * Subjects who were unwilling or unable to give written informed consent. * (If female) She was pregnant or breast-feeding. * (If female) She was of childbearing potential and she did not use an effective contraceptive method (double-barrier, intra-uterine device or abstinence) or she used oral contraceptives.