Development and characterisation of novel fentanyl-delta opioid receptor antagonist based bivalent ligands. - Bird, M. F.; Vardanyan, R. S.; Hruby, V. J.; Caló, G.; Guerrini, R.; Salvadori, S.; Trapella, C.; McDonald, J.; Rowbotham, D. J.; Lambert, D. G. (BJA: The British Journal of Anaesthesia, 2015)