Methylnaltrexone for opioid induced constipation

Endogenous opioid peptides are believed to mediate gastrointestinal motor activity and the transport of fluid and electrolytes via μ, kappa and sigma opioid receptors.¹ Opioid analgesics have multiple actions on intestinal function, including suppression of neuronal excitability, inhibition of excitatory and inhibitory neuronal inputs to gastrointestinal muscle and mucosa, reduced propulsive peristalsis and increased circular contractions, increased fluid absorption and depression of secretory activity. The net effect is to prolong the oral‐caecal transit time. Copyright © 2008 John Wiley & Sons, Ltd.