Portenoy, R.K., Thomas, J., Moehl-Boatwright, M.L., Tran, D., Galasso, F.L., Stambler, N., et al. (2008) Subcutaneous methylnaltrexone for the treatment of opioid-induced constipation in patients with advanced illness: A double-blind, randomized, parallel group, dose-ranging study. Journal of Pain and Symptom Management, 35, 458-468.