Antacids

Antacids, such as aluminium hydroxide, calcium carbonate, magnesium salts and sodium bicarbonate are widely used for the treatment of mild GORD, and are all available to buy over-the-counter.

Mode of action

All antacids have alkaline properties and relieve dyspepsia by chemically neutralising the stomach acid, and have also been shown to increase LOS pressure.[Higgs, 1974]

Different antacids vary considerably in their capacity to neutralise stomach acid, the rate at which they are expelled from the stomach, and the incidence of side effects (Table 1).

TABLE 1 – Profiles of different antacids

Type of antacid Profile of effects
Sodium bicarbonate

Rapidly acting, but often associated with rebound secretion of gastric acid, which cancels its effect.

Regular dosing (up to once an hour) is required to maintain the increase in stomach pH.

The excess sodium may result in alkaline urine and systemic alkalosis

Calcium carbonate

Rapidly acting but associated with even greater acid rebound than sodium bicarbonate. Insoluble calcium carbonate and stearate salts are formed, which can cause constipation.

'Milk-alkali' syndrome (excess calcium in the body) is also a common problem with repeated use

Magnesium trisilicate

Slower acting than other antacids, but with a more sustained effect.

This compound will result in the production of a silicon dioxide gelatinous adsorbent mass, which prolongs the antacid effect.

The magnesium in this preparation can cause diarrhoea

Aluminium hydroxide gel

Can form a protective layer in the stomach, and is particularly useful for the treatment of ulcers.

It has an astringent action but can also have a constipating effect when it reaches the colon.

Aluminium ions inhibit the activity of pepsin directly, as well as by raising the pH and preventing its activation.

Aluminium compounds can be constipating

Some antacid preparations contain a combination of compounds with the aim of reducing the adverse effects of the individual ingredients, for example, magnesium and aluminium compounds to reduce the risk of diarrhoea and constipation, respectively.

Many antacids contain other ingredients that modify the effects of the preparation. Antiflatulants, such as dimethicone and simethicone, break down gas bubbles in the stomach to reduce fullness and bloating. Such agents should not be co-prescribed with alginate reflux suppressants since they can destroy the raft by disrupting the bubbles of carbon dioxide that support its formation, and the aluminium or magnesium ions physically interfere with the gel structure. Activated charcoal may also be added to absorb gas and relieve bloating.

Efficacy

The primary indication for antacids is indigestion and general relief of stomach symptoms, but despite their widespread use, there is little evidence supporting their efficacy in GORD, with most data suggesting that antacids may be no more effective than placebo.[Graham & Patterson, 1983]

Dosing

Both liquid formulations and tablets are available. Because the acid neutralising capacity of an antacid depends upon the actual amount of alkaline salts it contains, large volumes of liquids or several tablets may need to be taken frequently throughout the day to control symptoms.

Adverse effects

Antacids are well tolerted in general, but a serious adverse effect is hypercalcaemia, which may occur after high, prolonged doses of calcium-containing antacids. It most commonly occurs as the ‘milk-alkali’ syndrome in ulcer sufferers who are taking calcium antacids and at the same time drinking large amounts of milk (which used to be recommended to relieve ulcer pain).

Other adverse effects are mainly limited to the lower GI tract. Diarrhoea or constipation may occur depending upon the particular formulation.

Precautions

Some antacids (especially aluminium compounds) form complexes with other drugs and interfere with their absorption or metabolism. Interactions with the tetracycline antibiotics, steroids and digoxin are a particular problem.

The release of drugs from enteric-coated preparations may also be affected; therefore, the timing of administration of antacids with preparations that have a delayed release in the body should be considered carefully.

In addition, to achieve any therapeutic benefit, antacids must be taken continually, because any resulting increase in stomach pH is a powerful stimulus for further acid production (rebound hypersecretion).

Additionally, many antacid formulations contain peppermint or spearmint, which are known aggravators of GORD.

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