Pharmacokinetics and ADME characterization of intravenous and oral [14C]-linerixibat in healthy male volunteers.

Linerixibat, an oral small molecule ileal bile acid transporter inhibitor under development for cholestatic pruritus in primary biliary cholangitis, was designed for minimal intestinal absorption (site of pharmacological action). This study characterized the pharmacokinetics, absorption, distribution, metabolism, and excretion of [14C]-linerixibat in humans following an intravenous microtracer, concomitant with unlabeled oral tablets, and [14C]-linerixibat oral solution. Linerixibat exhibited absorption-limited flip-flop kinetics: longer oral versus intravenous half-life (6-7 h vs 0.8 h). The short intravenous half-life was consistent with high systemic clearance (61.9 L/h) and low volume of distribution (16.3 L). In vitro studies predicted rapid hepatic clearance via cytochrome P450 (CYP) 3A4 metabolism, which deceptively predicted human hepatic clearance within 1.5-fold. However, linerixibat was minimally metabolized in humans after intravenous administration: ~80% elimination via biliary/fecal excretion (>90-97% as unchanged parent) and ~20% renal elimination by glomerular filtration (>97% as unchanged parent). Absolute oral bioavailability of linerixibat was exceedingly low (0.05%), primarily due to a very low fraction absorbed (0.167%; fgut~100%), with high hepatic extraction ratio (77.0%) acting as a secondary barrier to systemic exposure. Oral linerixibat was almost entirely excreted (>99% recovered radioactivity) in feces as unchanged and unabsorbed linerixibat. Consistent with the low oral fraction absorbed and ~20% renal recovery of intravenous [14C]-linerixibat, urinary elimination of orally administered radioactivity was negligible (<0.04% of dose). Linerixibat unequivocally exhibited minimal gastrointestinal absorption and oral systemic exposure. Linerixibat represents a unique example of high CYP3A4 clearance in vitro, but nearly complete excretion as unchanged parent drug via the biliary/fecal route. Significance Statement This study conclusively established minimal absorption and systemic exposure to orally administered linerixibat in humans. The small amount of linerixibat absorbed was eliminated efficiently as unchanged parent drug via the biliary/fecal route. The hepatic clearance mechanism was mis-predicted to be mediated via cytochrome P450 3A4 metabolism in vitro rather than biliary excretion of unchanged linerixibat in vivo.