A method of inhibiting MRP1 in a mammal which comprises administering to a mammal in need thereof an effective amount of a compound of formula I: ##STR16##where: A is ##STR17## ##STR18## or ##STR19## Y is --E--C(O)R.sup.1 or --E--NR.sup.2 R.sup.3 ; E is a bond or --CH.sub.2 --; R.sup.1 is independently at each occurrence hydrogen, C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.8 cycloalkyl, optionallysubs