The present invention provides a compound of the formula (I): ##STR00001##
(wherein, R.sup.1 is ethyl optionally substituted by halogen or amino
optionally substituted by lower alkyl, R.sup.2 and R.sup.3 are each
independently hydrogen or lower alkyl, X is cycloalkylene, lower alkylene
or piperidinediyl, Z is optionally substituted phenyl or optionally
substituted heterocyclyl) prodrug, pharmaceutically acceptable salt or
solvate thereof.