DIGESTIVE AGENTS are taken to mean any of a variety of agents that aid in some way the digestive process. (See also NUTRITIONAL AGENTS.)

Digestive enzymes may be given by mouth to make up deficiencies; e.g. chymotrypsin and pancreatin, which are currently used in human therapeutics to make up for deficiencies in secretions from the pancreatic exocrine gland (e.g. in cystic fibrosis and following pancreatectomy or chronic pancreatitis). They help digestion of starch, fat and protein. Cellulase was also once used, which is a concentrate of cellulose-splitting enzymes isolated from Aspergillus niger, and as a digestive adjunct. Papain, a purified proteolytic enzymic principle derived from Carica papaya, is essentially a vegetable pepsin. It is now not normally applied to food because of its adverse action on the gastrointestinal tract.

ANTACIDS are used to neutralize gastric acid, by raising gastric pH, so inhibiting peptic enzyme activity, which is greatly inhibited above pH 5. Although antacids are used to give symptomatic relief of dyspepsia, oesophagitis and gastritis, there is little objective evidence of accelerated healing of peptic ulcers (gastric or duodenal). Examples of antacids include aluminium hydroxide, calcium carbonate, magnesium carbonate, magnesium hydroxide, magnesium trisilicate and sodium bicarbonate.

Demulcents are agents or preparations that protect the mucous membranes and relieve pain and irritation. They are thought to work by forming a protective film and are commonly incorporated into antacid preparations for protecting the gastric mucosa of the mouth. The most commonly used is alginic acid or one of its alginate salts.

Carminatives and antifoaming agents (defoaming agents) help relieve flatulence, and are used to reduce gastric discomfort and colic. They may work by helping to bring up of wind, or erucation (belching). There are many agents used, but the mode of action or efficacy is not well established; examples include extracts or volatile oils of caraway, cardamom, camomile, cinnamon, cloves, dill, fennel, ginger, nutmeg and peppermint. A more recent approach is to use a polymer with a defoaming action agent, which helps gas coalesce, e.g. simethicone (a name for activated dimethicone).

Non-nutrient sweetening agents, with no calorific value, are widely used as sucrose substitutes. They are also valuable in masking unpalatable tastes, e.g. in oral liquid medicines. Examples include aspartame. cyclamates and saccharin.