SLC22A8 and chronic kidney disease: Therefore, we hypothesized that (i) dose-dependent competition between furosemide and selected PBUTs (IS, Kyn, PCS, IAA, and KA) for OAT1 and/or OAT3 leads to higher serum free UT concentrations in furosemide-treated patients with CKD than in those not treated with furosemide, and (ii) this difference is independent of other determinants of UT concentrations, such as the eGFR (Figure 1).