Otilonium bromide (OB) is a spasmolytic compound of the family of quaternary ammonium derivatives and has been successfully used in the treatment of patients with irritable bowel syndrome (IBS) due to its specific pharmacodynamic effects on motility patterns in the human colon and the contractility of colonic smooth muscle cells. This article examines how. OB inhibits the main patterns of human sigmoid motility in vitro, which are spontaneous rhythmic phasic contractions, smooth muscle tone, contractions induced by stimulation of excitatory motor neurons and contractions induced by direct effect of excitatory neurotransmitters. It does this mainly by blocking calcium influx through L-type calcium channels and interfering with mobilization of cellular calcium required for smooth muscle contraction, thereby limiting excessive intestinal contractility and abdominal cramping. OB also inhibits T-type calcium channels and muscarinic responses. Finally, OB inhibits tachykinin receptors on smooth muscle and primary afferent neurons which may have the joint effect of reducing motility and abdominal pain. All these mechanisms mediate the therapeutic effects of OB in patients with IBS and might be useful in patients with other spastic colonic motility disorders such as diverticular disease.
Keywords: L-type calcium channel; gastrointestinal motility; irritable bowel syndrome; otilonium bromide; smooth muscle relaxants; spasmolytics; tachykinin receptor; visceral sensitization.