<br>        Key Inclusion Criteria:<br><br>          -  A male or female patient with a clinical diagnosis of PFIC Type 1 or 2 and with a body<br>             weight above 5 kg<br><br>          -  Patient must have clinical genetic confirmation of PFIC-1 or PFIC-2<br><br>          -  Patient must have elevated s-BA concentration<br><br>          -  Patient must have history of significant pruritus and a caregiver reported observed<br>             scratching in the eDiary<br><br>          -  Patient and/or legal guardian must sign informed consent (and assent) as appropriate.<br><br>          -  Patients will be expected to have a consistent caregiver(s) for the duration of the<br>             study<br><br>          -  Caregivers and age-appropriate patients (=8 years of age) must be willing and able to<br>             use an eDiary device as required by the study<br><br>        Key Exclusion Criteria:<br><br>          -  Patient with pathologic variations of the ABCB11 gene that predict complete absence of<br>             the BSEP protein<br><br>          -  Patient with past medical history or ongoing presence of other types of liver disease<br>             including, but not limited to, the following:<br><br>               1. Biliary atresia of any kind<br><br>               2. Benign recurrent intrahepatic cholestasis, indicated by any history of normal s<br>                  BAs<br><br>               3. Suspected or proven liver cancer or metastasis to the liver on imaging studies<br><br>               4. Histopathology on liver biopsy that is suggestive of alternate non-PFIC related<br>                  etiology of cholestasis<br><br>          -  Patient with past medical history or ongoing chronic diarrhea<br><br>          -  Any patient with suspected or confirmed cancers except for basal cell carcinoma<br><br>          -  Patient with a past medical history of chronic kidney disease with an impaired renal<br>             function and a glomerular filtration rate <70 mL/min/1.73 m^2<br><br>          -  Patient with surgical history of disruption of the enterohepatic circulation (biliary<br>             diversion surgery) within 6 months prior to start of Screening Period<br><br>          -  Patient has had a liver transplant or a liver transplant is planned within 6 months of<br>             randomization<br><br>          -  Decompensated liver disease<br><br>          -  Patient suffers from uncontrolled, recalcitrant pruritic condition other than PFIC<br><br>          -  Patient who has been previously treated with an IBAT inhibitor whose pruritus has not<br>             responded to treatment<br>