This is an open-label, single-dose, sequentially designed, single-period study to determine the effect of moderate renal impairment on the pharmacokinetics (PK) of CTP-543 and its major metabolites following administration of a single 12 mg oral dose of CTP-543.

Inclusion Criteria:

• Adult males or females aged 18-75
• Body mass index (BMI) ≥ 18.0 and ≤ 42.0 kg/m2 at the time of screening
• If of reproductive age, willing and able to use a medically highly effective form of birth control 30 days prior to first dose, during the study and for 30 days following last dose of study medication
• Capable of giving informed consent and complying with study procedures

Additional Inclusion Criteria for Subjects with Renal Impairment:

• eGFR of 30-59 mL/minute/1.73 m2 as calculated by the MDRD equation
• No clinically significant change in disease status within the last 30 days before screening
• The subject must have a condition consistent with renal impairment and associated symptoms, but otherwise be determined to be in good health in the opinion of the Investigator
• Concomitant medications to treat underlying disease states or medical conditions related to renal impairment are allowed with the exception of strong CYP3A4 inhibitors and inducers

Exclusion Criteria:

• History of any clinically significant medical condition, psychiatric disease, social condition, or illness that might confound the results of the study or poses an additional risk to the subject by their participation in the study
• Known history of any gastrointestinal surgery or any condition possibly affecting drug absorption
• History of prolonged QT syndrome or a QTc interval with Fridericia's correction (QTcF) > 470 msec for males or QTcF > 480 msec for females at Screening visit
• Positive for human immunodeficiency virus, Hepatitis B virus, or Hepatitis C virus
• Females who are nursing or pregnant prior to drug administration
• Positive results for coronavirus infection (COVID-19) at screening or check-in
• Positive drugs of abuse or alcohol results at screening or check in (Day -1)

Additional Exclusion Criteria for Subjects with Renal Impairment:

• History of renal transplant
• Significant bleeding diathesis that could preclude multiple venipuncture or deep intramuscular injections
• Acute or exacerbating renal disease
• History of drugs of abuse or alcohol misuse within 6 months prior to screening
• Poorly controlled Type 1 or Type 2 diabetes