The purpose of the study was to To investigate whether the administration of BIA 6-512 (25 mg, 50 mg, 75 mg and 100 mg) at steady-state affects the pharmacokinetics of levodopa when administered in combination with a single-dose of immediate release levodopa/benserazide 200/50 mg or with a single-dose of immediate release levodopa/benserazide 200/50 mg plus a single-dose of entacapone 200 mg.

Single centre, double-blind, randomised, placebo-controlled, rising multiple-dose study in four sequential groups of healthy male and female subjects. Eligible subjects were admitted to the Human Pharmacology Unit (UFHBIAL - Portela & Cª, SA) on the day prior to receiving the first study medication. Starting in the morning of Day 1 (first dose), subjects received BIA 6-512/Placebo thrice-daily until the morning of Day 5 (last dose). Concomitantly with the morning dose of BIA 6-512/Placebo, on Day 4 a levodopa/benserazide 200/50 mg (Madopar® 250) single-dose was administered. On Day 5, a Madopar® 250 single-dose and a entacapone 200 mg (Comtan®) single-dose were administered concomitantly with the morning dose of BIA 6-512/Placebo. In the morning of Day 4 and Day 5, products were administered in fasting of at least 8 hours and subjects remained fasted until 2 h post-dose. Subjects were resident in the UFH from admission (Day 0) until at least 24 h post last dose (Day 6); then, they were discharged and returned for the follow-up visit.

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.