Drug and multidrug resistant modulators of the formula: ##STR1## where R.sup.1 and R.sup.2 are independently hydrogen or halo; A is --CH.sub.2 --CH.sub.2 --, --CH.sub.2 --CHR.sup.4 --CH.sub.2 --, or --CH.sub.2 --CHR.sup.5 --CHR.sup.6 --CH.sub.2 --, where R.sup.4 is --H, --OH, or acyloxy; one of R.sup.5 or R.sup.6 is --H, --OH, or acyloxy, and the other is --H; R.sup.3 is a polyaryl; and pharmaceutically acceptable salts and solvates thereof, are described and claimed. Use of the new compounds in the preparation of pharmaceutical compositions is described and claimed. In addition, methods for treating drug and multidrug resistance in various diseases using a compound, or pharmaceutically acceptable salt or solvate thereof, of this invention are described and claimed. Also, methods of enhancing oral bioavailability of a drug and methods of enhancing bioavailability of a drug to the brain using a compound, or pharmaceutically acceptable salt or solvate thereof, of this invention are described and claimed.
