Loperamide is an opiate which potently and selectively activates μ opioid receptors (Ki = 0.16 nM) exclusively in the periphery. Loperamide is an opiate which potently and selectively activates μ opioid receptors (Ki = 0.16 nM) exclusively in the periphery. It is a much weaker agonist of the δ opiod receptor (Ki = 50 nM). Through its actions in the gut wall, loperamide has antidiarrheal action by increasing transit time and by altering intestinal transport of water and electrolytes. It also blocks voltage-sensitive sodium channels (IC50 = 270 nM) and high voltage-activated calcium channels (IC50 = 900 nM), presumably through an inhibitory effect on calmodulin. Loperamide is comparable to morphine in blocking peripheral pain in rats.
