Compounds of the formula I: ##STR00001## or a pharmaceutically acceptable salt thereof, wherein, R.sup.1 is optionally substituted tetrazolyl, R.sup.2 is optionally substituted phenyl, optionally substituted pyridinyl or optionally substituted thienyl, and R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are as defined herein. Also provided are methods of using the compounds for treating diseases associated with the P2X.sub.3 and/or a P2X.sub.2/3 receptor antagonist and methods of making the compounds.