Amplification of ABCB1 was conducted with one PCR at 94°C, 2 min, 94°C 30 sec, 60°C 30 sec, 68°C 1 min 30 cycles, 4°C hold using the AccuPrime Taq DNA polymerase (Invitrogen, Carlsbad, CA). Primers used were forward 5’-GAGCCCATCCTGTTTGACTG-3’ and reverse 5’-ACTATAGGCCAGAGAGGCTGC-3´.