ANTACID

also spelled Antiacid, any substance, such as sodium bicarbonate, magnesium hydroxide, or aluminum hydroxide, used to counteract or neutralize gastric acids and relieve the discomfort caused by gastric acidity. Indigestion, gastritis, and several forms of ulcers are alleviated by the use of antacids. Numerous nonprescription liquid antacids reduce the acidity of indigestion or gastritis for up to three hours after a single dose. Of the many liquid antacids available, those consisting of either magnesium or aluminum alkalinizing agents are preferable to antacids containing calcium salts, which have been shown to lead to a secondary increase in gastric acidity. Antacids should be taken when gastric acidity is most likely to be increasing, namely, one hour and three hours after each meal and at bedtime. Although they are more convenient, antacid tablets are not nearly so effective as liquid forms. The usual dose of concentrated antacids is one tablespoon and of regular antacids twice that amount. Because magnesium-containing antacids tend to have a laxative effect if used regularly and aluminum-containing antacids tend to constipate, many patients prefer to alternate doses of the two types. Acid secretion itself can be reduced by the use of agents that block the action of histamine on the acid-secreting cells of the stomach. Two such agents, cimetidine (Tagamet) and ranitidine (Zantac), are quite effective and generally well-tolerated in full doses for at least two months and for longer periods at reduced dosage. In the treatment of ulcers, antacids may be used to neutralize hydrochloric acid and pepsin, to control pain, and even, in some cases, to promote healing. Not all antacids, however, are equally beneficial. Those that contain calcium may have undesirable side effects. Sodium bicarbonate should not be taken over long periods of time. Doctors should evaluate the antacids that they prescribe in order to be certain that the drugs do not contain excessive sodium for patients with high blood pressure or heart disorders. Patients with kidney disease should not take antacids that contain magnesium. A special group of drugs known as anticholinergics have been used for years to delay the emptying of the stomach. By doing so, they also diminish acid secretion and help to reduce the frequency and severity of ulcer pain. These drugs should also be carefully evaluated before they are prescribed. Individuals who have a tendency to develop glaucoma, who are markedly debilitated, who have an enlargement of the prostate gland, or who have difficulty urinating should not take anticholinergics.