^Wright, K. F.; Turner, C. R.; Jayasinghe-Beck, R.; Cohen, V. L.; Cheng, J. B.; Watson, J. W. (August 1997). "Differential in vivo and in vitro bronchorelaxant activities of CP-80,633, a selective phosphodiesterase 4 inhibitor". Can. J. Physiol. Pharmacol. 75 (8): 1001–8. doi:10.1139/y97-123. PMID9360015.