Physiological Pharmaceutics

The stomach 93Figure 5.15 The effect of time of day on the rate of gastric emptyingEffect of disease on gastric emptyingDiseases which affect gastric motility and emptying are predominantly diseases of thegastrointestinal tract itself, disorders involving smooth muscle and extraintestinal diseases.Some diseases only affect one of the phases of gastric emptying. Generally duodenal ulcerproduces accelerated emptying, while gastric ulcer reduces antral motility, producingnormal emptying of liquids but delayed emptying of solids 50 . Emptying of a solid meal isslowed in patients with pernicious anaemia 51 and atrophic gastritis 52 , but in achlorhydricpatients liquids empty rapidly 53 .Gastro-oesophageal reflux is a common disease affecting between 10 and 20% of thegeneral population 54 , although the true magnitude of the condition is not known since alarge proportion of sufferers self-medicate 55 . It is therefore likely that within a given patientgroup a significant proportion will be suffering from this disease to some extent. The effectof this disease on gastric emptying is unclear since some studies report no effect on theemptying of liquids 56 or mixed meals 57 , whilst others demonstrate a delay 58–60 . It is possiblethat the emptying of solids in a mixed meal is selectively delayed 61 suggesting impaired antralmotility. This would lead to a greater difference in emptying between liquids, pellets andtablets than in normal subjects.Migraine is frequently associated with nausea (95%) and vomiting (20%) and thereis some evidence that gastric emptying is delayed during migraine attacks.The eating disorders bulimia nervosa and anorexia nervosa are believed to affectbetween 5 and 10% of adolescent females and young women in the western world. Bulimiadoes not affect gastric emptying, but anorexia produces both delayed solid and liquidemptying 62 .DISPERSION OF DOSAGE FORMS IN THE STOMACHThe most commonly used type of dosage form is the conventional compressed tablet.Despite the use of scintigraphy to evaluate more sophisticated dose forms 63 , there has beensurprisingly little study of the behaviour of ordinary tablets. Most workers assume thattablets will disintegrate rapidly in vivo due to the use of superdisintegrants and the evidence