Study to Evaluate the Pharmacokinetics, Tolerability, and Safety of ACT-128800 in Japanese and Caucasian Healthy Male and Female Subjects

Inclusion Criteria: * Signed informed consent prior to any study-mandated procedure. * Japanese or Caucasian. (Japanese subjects: both parents of the subject are Japanese \[born in Japan\]. Caucasian subjects: both parents of the subject are Caucasian). * Body mass index between 18 and 28 kg/m\^2, inclusive. * Women not of childbearing potential: * Women of childbearing potential must have a negative serum pregnancy test at screening and a negative urine pregnancy test prior to drug intake on Day 1; use a reliable method of contraception and continue this contraception for the duration of the study and for at least 2 months after study drug intake. In addition, her partner must use a condom. * Systolic blood pressure 100-145 mmHg, diastolic blood pressure 50-90 mmHg, and heart rate (HR) 50-95 beats per minute (inclusive). * 12-lead electrocardiogram without clinically relevant abnormalities at screening. * Hematology and clinical chemistry results not deviating from the normal range to a clinically relevant extent at screening. * Negative results from urine drug screen at screening. * Ability to communicate well with the Investigator (if necessary with the help of an interpreter) and to understand and comply with the requirements of the study. Exclusion Criteria: * Electrocardiograph PQ/PR interval (time interval from the beginning of the P wave to the beginning of the QRS complex) \> 200 milliseconds at screening. * Nursing woman. * History of asthma or chronic obstructive pulmonary disease. * Known hypersensitivity to any excipients of the drug formulation. * Treatment with another investigational drug within 3 months prior to screening. * Excessive caffeine consumption, defined as \> 800 mg per day at screening. * History or clinical evidence of any disease and/or existence of any surgical or medical condition that might interfere with the absorption, distribution, metabolism or excretion of the study drug. * Any cardiac condition or illness, including ECG abnormalities, with a potential to increase the cardiac risk of the subject. * Smoking within the last month prior to screening. * Any immunosuppressive treatment within 6 weeks before study drug administration. * Previous treatment with any prescribed or over-the-counter medications within 2 weeks prior to screening. * Loss of 250 mL or more of blood within 3 months prior to screening. * Lymphopenia (\< 1,000 lymphocytes/μL). * Viral, fungal, bacterial or protozoal infection within 4 weeks before study drug administration. * Positive results from the hepatitis serology, except for vaccinated subjects, at screening. * Positive results from human immunodeficiency vrus serology at screening. * Legal incapacity or limited legal capacity at screening. * History of alcoholism or drug abuse. * Any circumstances or conditions, which, in the opinion of the investigator, may affect full participation in the study or compliance with the protocol.