Ponesimod, a selective S1P 1 receptor modulator, is a potential therapeutic agent for autoimmune disorders. The impact of hepatic or renal impairment on the pharmacokinetics, safety and tolerability of ponesimod and its inactive metabolites, ACT-204426 and ACT-338375, was evaluated. Two separate single-centre, open-label studies with 32 (hepatic study) and 24 (renal study) male and female individuals were conducted. Hepatic impairment was based on the Child-Pugh classification, and renal impairment was determined by creatinine clearance using the Cockcroft-Gault equation. Individuals with severe hepatic or renal impairment were to be matched (sex and body mass index) with healthy individuals. All individuals received a single dose of 10 mg ponesimod. For ponesimod, the ratio of geometric means of AUC 0-∞ for individuals with severe hepatic impairment versus healthy individuals was 3.07 (90% CI: 2.19, 4.32). For severely renally impaired individuals versus healthy individuals, this ratio was 1.14 (0.82, 1.58). C max and t max values of ponesimod were comparable across all groups in both studies. Exposure to metabolites was increased in individuals with moderate or severe hepatic impairment as compared to healthy individuals. During the course of these studies, there were no clinically relevant abnormalities related to vital signs, 12-lead electrocardiograms and clinical laboratory values. Sixteen adverse events (AEs) were reported, 12 of them of mild intensity. No AEs were considered to be treatment related. Overall, ponesimod was well tolerated. In individuals with renal function impairment, dose adjustment is not warranted, whereas the dose should be reduced in individuals with moderate and severe hepatic impairment.Multiple sclerosis (MS) is a global health concern, affecting approximately 2.5 million people worldwide. More than 200 people are newly diagnosed with MS every week in the United States [1][2][3]. MS is a chronic, autoimmune and neurodegenerative disease of the central nervous system (CNS) associated with irreversible progression of disability, physical and cognitive impairment, as well as fatigue, pain, depression and bladder dysfunction. Circulation of lymphocytes between blood, lymphatic system and non-lymphoid tissues is involved in the immune response inducing autoimmune diseases such as MS and psoriasis. Lymphocytes trafficking is tightly regulated, and it has been shown that the lysophospholipid sphingosine 1-phosphate (S1P) plays a central role in this mechanism. The pleiotropic effects of S1P are mediated by its cognate cell surface G-protein-coupled receptors (GPCRs), expressed on a wide range of cellular cell types and with five described subtypes, S1P 1-5 [4,5].Ponesimod, an iminothiazolidinone derivative, is a selective, reversible and potent orally available S1P 1 receptor modulator. Activation of S1P 1 GPCRs blocks the egress of lymphocytes from lymphoid organs and, as a consequence, reduces the number of circulating effector T cells driving the immune response. Thus, S1P 1...