The Effect of BIA 2-093 on the Steady-state Pharmacokinetic Profile of Phenytoin in Patients

Inclusion Criteria: * Male or female subjects aged between 18 and 65 years, inclusive. * Subjects who were on an established regimen of phenytoin monotherapy, which had been stable for at least 3 months. * Subjects who had clinical laboratory tests acceptable to the Investigator. * Subjects who were negative for hepatitis B surface antigen (HBsAg), hepatitis C virus (HCV) antibody (Ab) and human immunodeficiency viruses (HIV-1 and HIV-2) Ab tests at screening. * Subjects who were negative for alcohol and drugs of abuse at screening. * Subjects who were non-smokers or who smoked less than 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 or intrauterine device. * (If female) She had a negative pregnancy test at screening. Exclusion Criteria: * Subjects who did not conform to the above inclusion criteria. * Subjects who had a clinically relevant history or presence of any disease that may interfere with the pharmacokinetics or pharmacodynamics of the Investigational Products, or may affect its safety. * Subjects who had a history of relevant drug hypersensitivity. * Subjects who had a history of alcoholism or drug abuse in the last 2 years. * Subjects who consumed more than 21 units of alcohol a week. * Subjects who had one of the following findings on the electrocardiogram (ECG): sinus bradycardia, sinoatrial block, atrioventricular block of any degree. * Subjects who had a significant infection or known inflammatory process on screening and/or admission. * Subjects who had acute gastrointestinal symptoms at the time of screening and/or admission (e.g., nausea, vomiting, diarrhoea, heartburn). * Subjects who had used any drugs (other than phenytoin) that may affect the pharmacokinetic profile of the investigational products within 2 weeks of first dosing. * Subjects who had used any investigational drug and/or participated in any clinical trial within 3 months of their first admission to this study. * Subjects who had previously received ESL. * Subjects who had donated and/or received any blood or blood products within the previous 3 months prior to screening. * Subjects who were vegetarians, vegans and/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 gave written informed consent. * (If female) She was pregnant or breast-feeding. * (If female) She was of childbearing potential and she did not use an approved effective contraceptive method.