Anticholinergic
Anticholinergics (antimuscarinics, parasympatholytics) relieve pain by decreas-
ing GI motility and secretion and by inhibiting acetylcholine and blocking his-
tamine and hydrochloric acid. Anticholinergics delay gastric emptying time and
are used frequently to treat duodenal ulcers.
Anticholinergics should be taken before meals to decrease the acid secretion
that occurs with eating. They should not be taken with antacids because antacids
can slow the absorption of antichloinergic administration. Side effects include
dry mouth, decreased secretions, tachycardia, urinary retention, and constipa-
tion. However, because gastric emptying time is delayed, gastric secretions can
be stimulated and actually aggravate the ulceration.Antacids
Antacids promote ulcer healing by neutralizing hydrochloric acid and reducing
pepsin activity. Antacids don't coat the ulcer. There are two types of antacids:
Those that have a systemic effect and antacids without a systemic effect. A sys-
temic effect occurs when the antacid is absorbed.
Sodium bicarbonate is a systemic antacid that has many side effects including
sodium excess that causes hypernatremia and water retention. Sodium bicarbon-
ate also causes metabolic alkalosis related to the excess bicarbonate. Therefore,
sodium bicarbonate is seldom used to treat peptic ulcers.
Calcium carbonate is most effective in neutralizing acid, however one third
to one half of the drug can be systemically absorbed resulting in acid rebound.
Hypercalcemia and “milk-alkali syndrome” can result from excessive use of cal-
cium carbonate. Calcium carbonate is intensified if taken with milk products.
Nonsystemic antacids are composed of alkaline salts such as aluminum (alu-
minum hydroxide, aluminum carbonate) and magnesium (magnesium hydroxide,
magnesium carbonate, magnesium trisilicate, and magnesium phosphate). A small
degree of systemic absorption occurs with these drugs—mainly with aluminum.
Magnesium hydroxide has greater neutralizing power than aluminum hydrox-
ide, however magnesium compounds can be constipating in long-term use. A
combination of magnesium and aluminum salts neutralizes gastric acid without
causing constipation or severe diarrhea. Simethicone (an anti-gas agent) is found
in many antacids.Histamine2 (H2 blockers)
Histamine2 blockers prevent acid reflux in the esophagus by blocking the H2
receptors of the parietal cells in the stomach. This results in a reduction of(^342) CHAPTER 18 Gastrointestinal System