1. Bauer R, Czygan F-C, Franz G, Ihrig M, Nahrstedt A, Sprecher E. Demands on the quality of rationally applicable phytopharmaceuticals (in German). Dtsch Apoth Ztg. 1993;133:4105–1108.
2. Bauer R, Czygan F-C, Franz G, Ihrig M, Nahrstedt A, Sprecher E. Pharmaceutical quality, standardization and normalization of phytopharmaceuticals (in German). Z Phytother. 1994;15:82–91.
3. Bauer R, Tittel G. Quality assessment of herbal preparations as a precondition of pharmacological and clinical studies. Phytomedicine. 1996;2:193–198.
4. WHO. Research guidelines for evaluating the safety and efficacy of herbal medicines. World Health Organization, Regional Office for the Western Pacific, Manila; 1993.
5. Gaedcke F. Phytopharmaceuticals—Definition and explanation of important terms used in the judgement of their manufacturing process and quality (in German). Dtsch Apoth Ztg. 1991;131:2551–2555.