Bisheterocyclic derivative or salt thereof

A pharmaceutical composition which comprises a bisheterocyclic compound represented by the following formula (I) ##STR84## wherein R.sup.1 and R.sup.2 may be the same or different from each other and each represents a group of the formula:

• ##STR85## wherein R.sup.3 represents a hydrogen atom, X, Y.sup.1 and Y.sup.2 may be the same or different from one another and each represents an oxygen atom or a sulfur atom, B.sup.1 and B.sup.2 each represents a phenylene group, B.sup.3 represents a phenylene group, a naphthylene group, a cyclohexylene group or a furo[3,2-b]furanylene group, L.sup.1 and L.sup.2 each represents a group represented by the formula --(O).sub.n --A--, wherein n represents an integer of 0 or 1, and A represents a single bond or a lower alkylene group, provided that when n is 1, A represents a lower alkylene group and the oxygen atom of each of L.sup.1 and L.sup.2 is bonded to B.sup.3, or a stereoisomer thereof, a tautomer thereof, a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.