Kinetic analysis of saturable hepatic uptake of digoxin and its inhibition by rifampicin.
Although the organic anion transporter Oatp2 plays a critical role in determining the hepatic clearance of some drugs, little quantitative information exists about its functional characteristics in relation to inhibition of sinusoidal drug uptake. We investigated the uptake kinetics of the Oatp2 substrate digoxin in the isolated perfused rat liver. In the single-pass perfused liver three consecutive digoxin doses of 15, 30 and 45 micorg were administered in the presence or absence of rifampicin (100 micorM), an inhibitor of Oatp2. Digoxin was determined in the outflow samples by HPLC and all data were analyzed by simultaneous nonlinear regression assuming a Michaelis-Menten uptake mechanism. Hepatocellular uptake of digoxin was concentration-dependent with a Michaelis constant (K(M)) of 577.8 ng/ml. Rifampicin significantly reduced uptake (K(M) increased 2.5-fold) without affecting other parameters.
Section of Pharmacokinetics, Department of Pharmacology, Martin Luther University Halle-Wittenberg, D-06097 Halle, Saale, Germany. michael.weiss@medizin.uni-halle.de
Michael
M
Weiss
Daniel Y
DY
Hung
Klaus
K
Poenicke
Michael S
MS
Roberts
D000818:Animals; D004077:Digoxin / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008954:Models, Biological; D027361:Organic Anion Transporters / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010477:Perfusion; D051381:Rats; D017208:Rats, Wistar; D012293:Rifampin / Q000494:pharmacology*
D027361:Organic Anion Transporters; C503597:Slco1a4 protein, rat; D004077:Digoxin; D012293:Rifampin