Oral co-administration of elacridar (100 mg/kg, p.o.) and PF-02341066 increases the plasma and brain concentrations and brain-to-plasma ratios of PF-02341066 in wild-type mice, equaling the levels in Abcb1a/1b; Abcg2 mice. In friend leukemia virus stain B mice, the brain-to-plasm partition coefficient (Kp, brain) of elacridar is 0.82, 0.43, and 4.31 after intravenous (2.5 mg/kg), intraperitoneal (100 mg/kg), and oral (100 mg/kg) treatment, respectively. In Mrp4(-/-) mice, elacridar fully inhibits P-gp mediated transport of SKF 104864A, without siginificant effects on Bcrp1-mediated transport.