alkalosis which in short-term use may not cause symptoms. Sodium bicarbonate can release enough C02 in the stomach to cause discomfort and belching, which may or may not have a psychotherapeutic effect, according to the circumstances. Excess sodium intake may be undesirable in patients with cardiac or renal disease (see below).
Alginic acid may be combined with an antacid to encourage adherence of the mixture to the mucosa, e.g. for reflux oesophagitis.
Dimeticone is sometimes included in antacid mixtures as an antifoaming agent to reduce flatulence. It is a silicone polymer that lowers surface tension and allows the small bubbles of froth to coalesce into large bubbles that can more easily be passed up from the stomach or down from the colon. It helps distended mountaineers to belch usefully at high altitudes.
Adverse effects of antacid mixtures
Those that apply to individual antacids are described above but the following general points are also relevant.
Some antacid mixtures contain sodium, which may not be readily apparent from the name of the preparation. Thus they may be dangerous for patients with cardiac or renal disease. For example, a 10 ml dose of magnesium carbonate mixture or of magnesium trisilicate mixture contains about 6 mmol of sodium (normal daily dietary intake is approx. 120 mmol of sodium).
Aluminium- and magnesium-containing antacids may interfere with the absorption of other drugs by binding with them or by altering gastrointestinal pH or transit time. Reduced biological availability of iron, digoxin, warfarin and some NSAIDs has been ascribed to this type of interaction. It is probably advisable not to co-administer antacids with drugs that are intended for systemic effect by the oral route.
No single antacid is satisfactory for all circumstances and mixtures are often used. They may contain sodium bicarbonate for quickest effect, supplemented by magnesium hydroxide or carbonate. Sometimes magnesium trisilicate or aluminium hydroxide is added, but these are often used alone, though they are relatively slow-acting.
Disturbed bowel habit can be corrected by altering the proportions of magnesium salts, which cause diarrhoea, and aluminium salts, which constipate.
Tablets are more convenient for the patient at work but they act more slowly unless they are chewed; a liquid may be more acceptable for frequent use. Patients will find their own optimal pattern of use.
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