Intervention: Riboflavin
Trial phase: Phase 2
ATC code: A11HA04 | S01XA26
SMILES: Cc1cc2nc3c(=O)[nH]c(=O)nc-3n(C[C@H](O)[C@H](O)[C@H](O)CO)c2cc1C
Sex: All
Age groups: Adult | Older Adult
Healthy volunteers: No
Participants at risk: 78
Group description: Participants with CHB and moderate or severe renal impairment who were virologically suppressed and taking TDF, a TDF-containing anti-HBV regimen, or other OAVs, switched to TAF and received TAF 25 mg tablet once daily orally for 96 weeks.
Eligibility criteria:
Key Inclusion Criteria:

All Participants (Parts A and B):

Adult male or non-pregnant female individuals
Documented evidence of chronic HBV infection
Alanine aminotransferase (ALT) ≤ 10 × upper limit of normal (ULN)

Part A Only (renal impairment):

Maintained on TDF and/or other OAV treatment(s) for CHB for at least 48 weeks and with viral suppression (HBV deoxyribonucleic acid [DNA] < lower limit of quantitation [LLOQ]) for ≥ 6 months prior to screening

All individuals must have HBV DNA < 20 International units per milliliter (IU/mL) at screening by central laboratory
Both Hepatitis B e-Antigen (HBeAg) positive and negative individuals are eligible to participate
Moderate renal impairment (30 milliliters per minute [mL/min] ≤ estimated glomerular filtration rate by the cockcroft-gault formula [eGFRcg] ≤ 59 mL/min), severe renal impairment (15 mL/min ≤ eGFRcg < 30 mL/min) or end stage renal disease (ESRD) (eGFR < 15 mL/min) maintained on hemodialysis (HD)
Stable renal function (for participants with moderate or severe impairment): serum creatinine measured at least once within three months prior to screening. The measurement difference between the value measured within three months prior to screening versus the screening value must be ≤ 25% of the screening value

Part B Only (hepatic impairment):

Maintained on TDF and/or other OAV(s) for CHB for at least 48 weeks and with viral suppression (HBV DNA < LLOQ) for ≥ 6 months prior to screening

All individuals must have HBV DNA < 20 IU/mL at screening by central laboratory
Both HBeAg positive and negative individuals are eligible to participate
Child-pugh-turcotte (CPT) score of 7-12 (inclusive) OR a past history of CPT score ≥ 7 and any CPT score ≤ 12 at screening
eGFRCG ≥ 30 mL/min using the Cockcroft-Gault equation

Key Exclusion Criteria:

All Individuals (Parts A & B):

Women who are breastfeeding or who believe they may wish to become pregnant during the course of the study
Males and females of reproductive potential who are unwilling to use an "effective", protocol-specified method(s) of contraception during the study
Co-infection with hepatitis C virus (HCV), human immunodeficiency virus (HIV), or hepatitis D virus (HDV)
Prior Interferon (IFN) use within 6 months of screening
Evidence of hepatocellular carcinoma
Received solid organ or bone marrow transplant
Significant cardiovascular, pulmonary, or neurological disease
Malignancy within 5 years prior to screening, with the exception of specific cancers that are cured by surgical resection (basal cell skin cancer, etc.). Individuals under evaluation for possible malignancy are not eligible
Currently receiving therapy with immunomodulators (e.g. corticosteroids), nephrotoxic agents, or agents capable of modifying renal excretion
Known hypersensitivity to study drugs, metabolites, or formulation excipients
Current alcohol or substance abuse judged by the investigator to potentially interfere with individual's compliance
Any other clinical condition or prior therapy that, in the opinion of the Investigator, would make the individual unsuitable for the study or unable to comply with dosing requirements.

Part A Only (Renal Impairment):

Current or historical evidence of clinical hepatic decompensation (e.g., ascites, encephalopathy or variceal hemorrhage)

Abnormal hematological and biochemical parameters, including:

Hemoglobin < 9 grams per deciliter (g/dL)
Absolute neutrophil count < 750/cubic millimeter (mm^3)
Platelets ≤ 50,000/mm^3
Aspartate aminotransferase (AST) > 10 × ULN
Albumin < 3.0 g/dL
Total bilirubin > 2.5 × ULN
International normalized ratio of prothrombin time (INR) > 1.5 × ULN (unless stable on anticoagulant regimen)
Individuals with ESRD (i.e. eGFRcg < 15 mL/min) not on HD, or those on other forms of renal replacement therapy (i.e. peritoneal dialysis)

Part B Only (Hepatic Impairment):

Active variceal bleeding within 6 months or prior placement of a portosystemic shunt (such as transjugular intrahepatic portosystemic shunt [TIPS])
History of hepatorenal syndrome, hepatopulmonary syndrome, Grade 3 or Grade 4 hepatic encephalopathy, or spontaneous bacterial peritonitis within 6 months of screening
Grade 2 hepatic encephalopathy at screening
Model for end-stage liver disease (MELD) score ≥ 30

Abnormal hematological and biochemical parameters, including

Absolute neutrophil count < 750/mm^3
Platelets < 30,000/mm^3
Hemoglobin < 8.0 g/dL

Note: Other protocol defined Inclusion/Exclusion criteria may apply.