^Christiane Pauli-Magnus, Oliver von Richter, Oliver Burk, Anja Ziegler, Thomas Mettang, Michel Eichelbaum and Martin F. Fromm (2000). "Characterization of the Major Metabolites of Verapamil as Substrates and Inhibitors of P-glycoprotein". Journal of Pharmacology and Experimental Therapeutics. 293 (2): 376–382. PMID10773005.{{cite journal}}: CS1 maint: multiple names: authors list (link)