Tenofovir Exposures in Advanced Kidney Disease Study

Inclusion Criteria: * Capable of giving informed consent * Male or female aged 18 years or older * A history of chronic kidney disease (eGFR \<45 for at least 3 months) currently not requiring haemodialysis or peritoneal dialysis * Current eGFR \<30 based on serum creatinine measurement and calculated with the CKD-EPI (2021) formula \[6\] * Up to 20 individuals with eGFR 30-44 will be included; such participants require prior CI approval to ensure at least 30 participants with eGFR \<30 can be enrolled * Stable ART regimen (consistent use for at least 3 months) * ART regimens must contain TAF (administered at standard dose \[25mg once daily as part of unboosted regimens; 10 mg once daily as part of ritonavir- or cobicistat-boosted regimens\]) and FTC, with any additional retrovirals allowed * Agreeable to accommodate morning TAF/FTC dosing schedule for one week prior to undergoing the pharmacokinetic assessments * Well controlled HIV for \>6 months * All available HIV RNA measurements \<200 copies/mL * Stable clinical condition Exclusion Criteria: * Dialysis at screening, Day 1, or in the past 90 days prior to Day 1 * ART switch in the past 3 months * Individuals on ART regimens not containing TAF/FTC, or non-standard doses of TAF/FTC are excluded * Uncontrolled HIV (HIV RNA \>200 copies/mL) or active hepatitis C (HCV RNA positive) in the past 6 months * Hb \<80 g/L or eGFR \>45 or HIV RNA \>200 copies/mL at screening * Medications that induce TAF or FTC metabolism, e.g. rifamycins, phenytoin, St Johns Wort * Current or recent use of entecavir (past 30 days) * Current or recent (past 30 days) acute clinical complications (e.g. hospitalizations, severe infections or acute graft rejection) * Pregnancy or lactation (female participants only)