tetracyclic tetracyclic tetracyclics are cyclic chemical compounds that contain four fused rings of atoms, for example, tröger's base. doxycycline, a tetracyclic antibiotic. mirtazapine, a tetracyclic antidepressant. some tricyclic compounds having three fused and one tethered ring (connected to main nucleus by a single bond) can also classified as tetracyclic, for example, ciclazindol. tetracyclic compounds have various pharmaceutical uses, such as: tetracycline antibiotics doxycycline tigecycline omadacycline eravacycline tetracyclic antidepressants benzoctamine loxapine mazindol mianserin mirtazapine