Citation Select	Felden Pharmazentrum frankfurt/ZAFES, Institute of Clinical Pharmacology, Johann Wolfgang Goethe-University, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany., Walter C, Harder S, Treede RD, Kayser H, Drover D, Geisslinger G, Lötsch J Comparative clinical effects of hydromorphone and morphine: a meta-analysis Br J Anaesth. 2011 Sep;107(3):319-28