US 6974820 which cites US 3480626 and Bertholdt H, Pfleger R, Schulz W (1967). "[On azoniaspire-compounds. 2. Preparation of esterified azoniaspire-compounds of nortropan-3-alpha- or 3-beta-ol (1)]". Arzneimittelforschung. 17 (6): 719–26. PMID5632538.
Peretto I, Petrillo P, Imbimbo BP (November 2009). "Medicinal chemistry and therapeutic potential of muscarinic M3 antagonists". Med Res Rev. 29 (6): 867–902. doi:10.1002/med.20158. PMID19399831.
Pak RW, Petrou SP, Staskin DR (December 2003). "Trospium chloride: a quaternary amine with unique pharmacologic properties". Curr Urol Rep. 4 (6): 436–440. doi:10.1007/s11934-003-0023-1. PMID14622495.
Rosa GM, Bauckneht M, Scala C, Tafi E, Leone Roberti Maggiore U, Ferrero S, et al. (November 2013). "Cardiovascular effects of antimuscarinic agents in overactive bladder". Expert Opin Drug Saf. 12 (6): 815–827. doi:10.1517/14740338.2013.813016. PMID23800037.
DE patent 1194422, Bertholdt H, Pfleger R, Schulz W, "[Verfahren zur Herstellung von Azoniaspironortropanderivaten] (A process for preparing azonia-spirono-tropane derivatives)", issued 10 June 1965, assigned to Dr. Robert Pfleger Chemische Fabrik GmbH
Peretto I, Petrillo P, Imbimbo BP (November 2009). "Medicinal chemistry and therapeutic potential of muscarinic M3 antagonists". Med Res Rev. 29 (6): 867–902. doi:10.1002/med.20158. PMID19399831.
Pak RW, Petrou SP, Staskin DR (December 2003). "Trospium chloride: a quaternary amine with unique pharmacologic properties". Curr Urol Rep. 4 (6): 436–440. doi:10.1007/s11934-003-0023-1. PMID14622495.
Rosa GM, Bauckneht M, Scala C, Tafi E, Leone Roberti Maggiore U, Ferrero S, et al. (November 2013). "Cardiovascular effects of antimuscarinic agents in overactive bladder". Expert Opin Drug Saf. 12 (6): 815–827. doi:10.1517/14740338.2013.813016. PMID23800037.
US 6974820 which cites US 3480626 and Bertholdt H, Pfleger R, Schulz W (1967). "[On azoniaspire-compounds. 2. Preparation of esterified azoniaspire-compounds of nortropan-3-alpha- or 3-beta-ol (1)]". Arzneimittelforschung. 17 (6): 719–26. PMID5632538.