21.5: Acid Suppressive Drugs for Peptic Ulcer Disease: Antacids

In the complex environment of the gastric lumen, excessive acid secretion can lead to the formation or worsening of ulcers within the delicate mucosal layer. Antacids, such as sodium bicarbonate and calcium carbonate, provide relief by neutralizing this acid, transforming it into harmless salt and water. This neutralization process raises the gastric pH from a highly acidic level of 1 to a more basic 3-4, reducing the acidity within the stomach.

However, this neutralization reaction between antacids and gastric acid produces carbon dioxide (CO₂). Accumulation of CO₂ can lead to stomach distention and belching, causing discomfort. Furthermore, excessive doses of antacids can result in the absorption of unreacted alkali. This absorption raises the alkalinity of the blood, leading to a condition known as metabolic alkalosis.

Magaldrate, a hydroxymagnesium aluminate complex, is employed to address these side effects. Magaldrate transforms into poorly absorbed magnesium and aluminum hydroxides in the stomach's acidic environment. This transformation imparts a sustained antacid effect, mitigating the discomfort caused by excessive CO₂ production.

It's important to note that the efficiency of antacids hinges on several factors, including their dissolution rate, water solubility, reaction speed with gastric acid, and gastric emptying rate. Interestingly, the clearance of antacids is faster on an empty stomach. However, when taken with food, their duration of action is prolonged, providing a longer-lasting relief from gastric discomfort.

Antacids are pivotal in the delicate balance between neutralizing gastric acidity and avoiding unwanted side effects.

In the gastric lumen, increased acid secretion can form or exacerbate ulcers in the mucosal layer.

Carbonate antacids, like sodium bicarbonate and calcium carbonate, can neutralize this acid, forming salt and water. This raises gastric pH from 1 to 5 and reduces intragastric acidity.

However, the reaction of these antacids with gastric acid also generates CO₂, which, upon accumulation, causes stomach distention and belching.

Additionally, excessive doses of these antacids lead to absorption of unreacted alkali, raising blood's alkalinity and causing metabolic alkalosis.

Moreover, sodium load increases fluid retention in hypertensive patients, while calcium triggers rebound acid secretion.

To mitigate the side effects, magaldrate, a hydroxymagnesium aluminate complex is used.

In gastric acid, it converts into poorly absorbed magnesium and aluminum hydroxides, imparting a sustained antacid effect.

The efficiency of antacids depends on dissolution rate, water solubility, reaction speed with acid, and gastric emptying rate.

Their clearance is faster on an empty stomach, but when taken with food, their duration of action is prolonged.