A method of treatment of migraine, cluster headaches and trigeminal neuralgia, radiation or cytotoxic agent induced nausea and vomiting and/or cardiac arrhythmia in mammals, including humans, which method comprises administering an effective amount of a compound of formula (I) or a pharmaceutically acceptable salt thereof: ##STR1## wherein: R.sub.1 is C.sub.1-6 alkyl;R.sub.2 is amino or C.sub.1-7 acylamino;R.sub.3 is halo;one of R.sub.4 and R.sub.5 is hydrogen, C.sub.1-6 alkyl, phenyl or phenyl C.sub.1-3 alkyl, which phenyl moieties may be substituted by one or more substituents selected from C.sub.1-6 alkyl, C.sub.1-6 alkoxy, CF.sub.3 or halogen;the other of R.sub.4 and R.sub.5 is hydrogen or C.sub.1-6 alkyl;p is 0 to 2; andq is 0 to 3.