A polycyclic heterocyclic compound has the formula ##STR1## wherein n is 1 or 2, R.sub.1 represents (i) lower alkyl, (ii)--CH.sub.2 OH or (iii) ##STR2## R.sub.2 represents (a) hydrogen, (b) ##STR3## or (c)--OR.sub.3, R.sub.3 represents hydrogen, C.sub.1 -C.sub.20 alkyl mono or polyhydroxyalkyl, aryl or aralkyl optionally substituted, the residue of a sugar or wherein p is 1, 2, or 3, and r' and r" represent hydrogen, lower alkyl, mono or polyhydroxalkyl, aryl optionally substituted, amino acid residue, aminated sugar residue, or together form a heterocycle, X represents oxygen, sulfur, SO, SO.sub.2 or --NR.sub.4, Y represents CR.sub.4 or a nitrogen atom and R.sub.4 represents hydrogen or lower alkyl. This polycyclic heterocyclic compound can be used in human and veterinary medicine and especially in the topical or systemic treatment of determatologic diseases.