A method of treating an anthrax infection wherein a compound of formula I ##STR00001## wherein R.sup.1 and R.sup.2 represent, independently of one another unsubstituted or specifically substituted C.sub.1-4alkoxy; and R.sup.3 represents hydrogen; cyano; unsubstituted or specifically substituted C.sub.1-6alkyl; C.sub.3-6cycloalkyl; C.sub.2-6alkenyl; C.sub.7-18bicyclyl; aryl, aryl-C.sub.1-4alkyl, aryl-Q-C.sub.1-4alkyl heteroaryl, heterocyclyl or heterocyclyl-C.sub.1-6alkyl, wherein aryl denotes a mono- or poly-nucleous group with 6 to 14 ring carbon atoms; heterocyclyl denotes a 4- to 6-membered non-aromatic heterocyclic group comprising 1 to 3, nitrogen, oxygen and/or sulfur atoms; heteroaryl denotes a mono- or polynuclear heteroaromatic group consisting 5- and/or 6-membered rings and comprising 5 to 13 carbon atoms and 1 to 4, nitrogen, oxygen and/or sulfur atoms; and Q means --SO-- or --SO.sub.2--; or a pharmaceutically acceptable salt, solvate or hydrate or a prodrug thereof; is administered to said subject in a quantity effective to inhibit, suppress, or expel an anthrax infection in said subject.