Gastrointestinal tract delayed emptying

The gastrointestinal tract is the only system outside the central nervous system (CNS) with significant concentrations of opioid receptors. This reflects their common embryonic origins. Opioids increase intestinal tone and decrease propulsive peristalsis, resulting in delayed gastric emptying and constipation or ileus. Opioids increase common bile duct pressure and decrease bile production and flow, primarily because of spasm of the sphincter of Oddi. The tone of the bile duct itself is also increased. 

Additive effect. Delayed gastric emptying may cause more levodopa to be metabolized within the wall of the gastrointestinal tract. Antimuscarinic effects i saliva production, which i dissolution of the tablet... 

Among factors that may modify gastrointestinal absorption of ingested chemicals, the presence of food in the tract is one of the most important. The presence of food in the stomach will delay the absorption of weak organic acids at that site. The presence of lipid-rich food will delay the emptying of the gastric content into the intestine and thus also delay the absorption of chemicals. Conversely, an empty stomach facilitates absorption, a situation that is almost always beneficial in drug therapy. 

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