Gastric emptying: factors affecting

Physiological factors affecting absorption, for example, gastrointestinal (Gl) transit time, gastric emptying time, Gl content, surface area, pH, enzymatic metabolism, and site-speciLc absorption... 

The process of gastric emptying is extremely complex and is influenced by many factors such as presence of food, food content, pH, and posture. Most drugs are not absorbed from the stomach and are therefore dependent on the gastric emptying process to deliver them to their site of absorption. Consequently, the process and factors that affect it have been extensively studied with many conflicting views reported. 

The sensitivity and specificity of these tests are limited by the complexity of the processes of absorption and metabolism. The substrates are specific for pancreatic lipases and the product is absorbed independently of micelle formation, but the results of the test are affected by other factors, such as gastric emptying, mucosal absorption, hepatic metabolism, endogenous "CO2, and total CO2 production. These factors may explain the test s limited diagnostic sensitivity in mild and moderate pancreatic insufficiency and its lack of specificity in nonpancreatic GI diseases. 

The variability seen in the absorption of orally administered drugs is mainly due to different rates of gastric emptying, which are affected by the various factors listed above. Hence, to minimize variability, bioavailability studies may be conducted under controlled conditions, such as healthy individuals of controlled weight and age under fasted conditions or with a controlled diet. The use of healthy subjects minimizes both inter-and intrasubject variability. 

Many studies have been carried out since the late 1980s in attempts to correlate in vitro dissolution with in vivo performance. Some studies have found a significant correlation whereas others have been unsuccessful. This limited success in establishing a quantitative correlation is attributed to the fact that absorption is a complicated process. Physiological factors such as gastric emptying time, metabolism of drug by gut wall enzymes or intestinal microflora, and the hepatic first-pass effect can affect the absorption process. 

The major gastric factor that affects motility and the rate of emptying is the volume of chyme in the stomach. As the volume of chyme increases, the wall of the stomach becomes distended and mechanoreceptors are stimulated. This elicits reflexes that enhance gastric motility by way of the intrinsic and vagus nerves. The release of the hormone gastrin from the antral region of the stomach further contributes to enhanced motility. 

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