Compounds of the formula (I), or pharmaceutically acceptable salts thereof ##STR1## wherein X is phenyl, optionally substituted by one halogen, C.sub.1-4 alkyl or C.sub.1-4 alkoxy; or pyridyl; R.sub.1 is hydrogen or C.sub.1-6 alkyl; and n is 1 to 6, pharmaceutical compositions containing them and a process for their preparation. These compounds are useful in the prophylaxis or treatment of diseases due to a histamine-mediated allergic response.