He L., Kim J., Ou C., et al. Methadone antinociception is dependent on peripheral opioid receptors. J Pain.2009;10(4):369-379.
2.
Holzer P.Opioid receptors in the gastrointestinal tract. Regul Pept.2009;155(1-3):11-17.
3.
Wirz S., Wittmann M., Schenk M., et al. Gastrointestinal symptoms under opioid therapy: a prospective comparison of oral sustained-release hydromorphone, transdermal fentanyl, and transdermal buprenorphine. Eur J Pain.2009;13(7):737-743.