Synonyms in a broader sense

  • Sodium hydrogen carbonate
  • Calcium carbonate
  • Magnesium carbonate
  • Algeldrat
  • Hydrotalcite
  • Magaldrate
  • Maaloxan
  • Progastrite
  • Ancid
  • Megalac
  • Talcid
  • Riopan
  • Simaphil


Antacids (anti = against; lat. acidum = acid) are drugs that bind stomach acid. Antacids are mainly used to treat heartburn and stomach acid-related complaints. Antacids are a relatively old group of drugs that have been developed over time and not only neutralise stomach acid but also protect the stomach lining.

Active principle

The effect of acids can be neutralized by adding so-called bases (e.g. antacids). This chemical principle is the basis of the antacid effect. Excess stomach acid (see reflux disease) is immediately neutralised when an antacid, for example in the form of a tablet, reaches the stomach. The individual preparations sometimes differ considerably in their acid-binding capacity and the sustainability of their effect.

Fields of application of antacids

The main application for antacids is the symptomatic treatment of mild, occasionally occurring acid-related stomach complaints and heartburn. They are freely available in pharmacies and can be dosed as required. Antacids are available either in solid form as chewable tablets or in liquid form as suspensions.

If the symptoms are still present after an application period of 4-8 days, you should consult a doctor to clarify the cause. Frequent complaints are usually symptoms of an underlying disease requiring therapy. Antacids are therefore not suitable for long-term therapy.

However, antacids may be used without any problems for a transitional period to alleviate acute complaints until a causal therapy has been initiated by the doctor. In the case of diseases such as inflammation of the mucous membranes of the stomach, inflammation of the oesophagus or peptic ulcers, where a reduction in the acidity of the gastric juice is also desired, however, antacids are only rarely used. In these cases, so-called proton pump inhibitors are now the first choice.

Traditional and modern antacids

The product range of gastric acid binding preparations is diverse. There are single active ingredients and more effective preparations with combinations of active ingredients. The effectiveness has been constantly improved over the years and undesirable side effects have been reduced.

A modern antacid not only has a high acid binding capacity, but usually also a mucous membrane protecting effect. The advantages in the application of a modern antacid have increasingly displaced the traditional preparations. Active agents: e.g. sodium hydrogen carbonate, calcium carbonate, magnesium carbonate Active agents of traditional antacids are relatively unstable.

Their effect starts immediately in the stomach. They neutralize existing acid very quickly. As a result, the pH value in the stomach rises strongly after taking traditional antacids.

However, this is only desirable up to certain values, as otherwise the function of digestive enzymes is impaired. – Traditional antacids

In addition, a too high pH value favours the so-called “rebound effect”. This describes the phenomenon that the stomach is forced to produce more acid when the pH value is outside the natural acidic environment (pH 1- 5).

Modern antacids have a buffering function, i.e. they prevent the pH value from rising to values > 4. This minimises the rebound effect, does not significantly impair the function of the digestive enzymes and maintains the stomach’s acid protective function against pathogens. A disadvantage of using carbonates as antacids is gas evolution.

The reaction between carbonates and stomach acid produces carbon dioxide, which as a gas can cause unpleasant side effects such as belching, flatulence or a feeling of fullness. With modern antacids there is no gas development. Traditional antacids are still available in pharmacies and drugstores, but are no longer the first choice.

Active ingredients: algeldrat, hydrotalcite, magaldrate A modern antacid is characterised on the one hand by the fact that it contains several active ingredients. These active ingredients are arranged in layers and give the tablet a special stability and flexibility in the release of the active ingredient. During the neutralisation of gastric acid, no gas is released, as with carbonates.

Moreover, modern antacids only dissolve in the presence of acid. If too little acid is present, no active ingredient is released. Thus, the pH value is kept constant in a slightly acidic environment in order not to impair the digestive enzymes.

This is known as a buffering effect. The active ingredient is released slowly and always only in the quantity that is currently required. This means that modern antacids react more flexibly to acid reproduction than traditional active ingredients.

These unfold their full effect within a short period of time and thus have no lasting effect. Algeldrat (trade names include Maaloxan®, Progastrit®) Algeldrat is another name for hydrous aluminum hydroxide. As an antacid it is usually combined with magnesium hydroxide.

When stomach acid is neutralized, no gas is produced, but water in small quantities. Preparations with the active substance combination of aluminium hydroxide and magnesium hydroxide have a neutralisation capacity of 25 mval. Hydrotalcite (trade names include Ancid®, Megalac®, Talcid®) Hydrotalcite is a naturally occurring mineral.

However, nowadays it is produced synthetically. Hydrotalcite is a mixture of the salts magnesium hydroxide, aluminium hydroxide, carbonate and water. Its special feature is its arrangement, also known as a layered lattice structure.

The edge layers of the tablet consist alternately of magnesium and aluminium salts. Carbonate and water are located inside. The edge layers gradually react with the gastric acid and neutralise it.

The less acid is present, the less soluble the active ingredient is. If the acid content in the stomach drops (> pH 4), the active ingredient can hardly be dissolved from the tablet (buffer function). If the stomach produces acid again, the pH value drops and more active ingredient is released.

Hydrotalcid is therefore very flexible. Furthermore, Hydrotalcite can protect the stomach lining, e.g. from damage by NSAIDs. The gastric mucosa contains so-called bicarbonate ions as a protective factor.

Hydrotalcite is a bicarbonate ion accumulator and can release them when needed. The neutralisation capacity of hydrotalcite is 26 mval. Magaldrate (trade names among others Riopan®, Simaphil®) Magaldrate is also an active ingredient with a layered lattice structure.

It is composed of aluminium and magnesium hydroxide as well as sulphate ions. Due to its structure, magaldrate, like hydrotalcite, can react very flexibly to the post-production of stomach acid. The neutralization capacity of Magaldrat is 22.6 mval. – Modern Antacids