This invention provides a method of treating pain in a mammal that includes administering to a mammal in need of such treatment a pain treating effective amount of a compound of the formula I: or a pharmaceutically acceptable salt thereof, wherein each of R.sup.1, R.sup.2, R.sup.3, n, y, and Ar is as defined and described herein. The present invention also provides pharmaceutical compositions for treating pain containing a pain treating effective amount of the compound of formula I.