Systemic exposure to orally administered digoxin is increased by coadministration of MDR1 inducers and negatively correlated with MDR1 protein expression in the intestine. MDR1 is also expressed on the brush-border membrane of renal epithelia, and its function can be monitored using digoxin (>70% excreted in the urine). MDR1 inhibitors (e.g., quinidine, verapamil, vaspo-dar, spironolactone, clarithromycin, and ritonavir) all markedly reduce renal digoxin excretion. In view of this, drugs with narrow therapeutic windows (e.g., digoxin) should be used with great care if MDR1-based drug-drug interactions are likely.
ABC Transporters Involved in Drug Absorption, Distribution, and Excretion
Transporter Name Tissue Distribution
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