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H2 receptor antagonists – effect, application & risks

H2 receptor antagonists

H2 receptor antagonists are drugs that inhibit gastric acid production. As antihistamines , they block the binding of histamine to the H2 receptors of the parietal cells of the stomach . In addition to proton pump inhibitors , they are often used in gastric and duodenal ulcers and in reflux disease .

What are H2 receptor antagonists?

H2-receptor antagonists compete with histamine to occupy the H2-receptors of the parietal cells. They are medicines that limit the production of gastric acid. Therefore, they are used in addition to proton pump inhibitors for severe gastric and duodenal ulcers.

Furthermore, the H2-receptor antagonists are also used in reflux disease. In reflux disease, stomach acid enters the esophagus due to a malfunction in the sphincter muscle between the esophagus ( gullet ) and the stomach. This reflux of acid in the stomach is noticeable through heartburn .

By inhibiting gastric acid production, the reflux of gastric acid is also greatly reduced. At night, gastric acid production is reduced by up to 90 percent when H2 receptor antagonists are used. However, their effectiveness when ingested is only about 50 percent.

Although H2-receptor antagonists reduce hydrochloric acid production and the secretion of the enzyme pepsin in the stomach, they cannot eliminate the cause of the increased acid production. With their help, however, the negative effects of acid on the stomach, duodenum and esophagus can be contained.

Possible causes of increased gastric acid production include the activity of the gastric bacteria Helicobacter pylori or hormonal disorders such as Ellison-Zollinger syndrome. H2 receptor antagonists do not have a uniform chemical structure, but only a common function. They bind to H2 receptors and can thus block histamine from binding to these receptors.

Pharmacological action

The main effect of H2-receptor antagonists on the organism is to compete with histamine in occupying the H2-receptors. Histamine is a tissue hormone that plays a major role in many physiological processes in the body. It is found everywhere in the body and exerts its effect by binding to the histamine receptors H1, H2, H3 or H4.

In addition to its function as a mediator in inflammatory reactions, it is also responsible for acid formation in the stomach. It binds to the H2 receptors of the parietal cells of the stomach to form and secrete gastric acid and pepsin.

The effect of the H2 receptor antagonists is to block as many receptors as possible from binding with histamine. Although the H2 receptor antagonists bind to the H2 receptors, they do not trigger the production of gastric acid or pepsin. The fewer H2 receptors available for histamine, the less gastric acid can be formed.

Medical Application & Use

In addition to proton pump inhibitors, H2 receptor antagonists are also widely used to treat gastric ulcers and heartburn. They are somewhat less effective against increased acid formation in the stomach than proton pump inhibitors.

The drug class of H2-receptor antagonists is represented today by the drugs cimetidine , ranitidine , famotidine , roxatidine, nizatidine or lafutidine. Cimetidine was the first drug of these active ingredients and was launched in the 1970s. Due to frequent side effects and the disruption of the metabolism of many drugs, it has now been largely replaced by other active ingredients with the same function.

Each H2-receptor antagonist shows an individual potency. Famoditin has proven to be the most effective. While only 40 milligrams are required for the same effect, 300 milligrams have to be used for nizatidine and raniditin. Cimetidine even requires 800 milligrams for the same effects. For this reason, stronger side effects develop when using it.

The duration of action of the individual H2 receptor antagonists also varies. Famotidine has the longest duration of action at twelve hours. With the other H2-receptor antagonists, the duration of the effect is between four and six hours. The application of these active ingredients is intended to prevent the harmful influence of the acid on the stomach, duodenum or esophagus.

Stomach acid, in particular, can further destroy the bacterially damaged lining of the stomach and duodenum, thereby forming the basis for ulcers . There is no protective mucosal layer in the esophagus. If the stomach acid gets there, it results in an immediate chemical burn, which manifests itself as heartburn.

Although H2-receptor antagonists do not directly protect the mucous membranes of the stomach, duodenum and esophagus, they reduce the harmful influence of gastric acid by reducing its concentration in the stomach.

Risks & side effects

However, side effects can also be expected when taking H2-receptor antagonists. Since cimetidine only develops its effect when high concentrations are used, this is also where the strongest side effects occur. Hypersensitivity can cause headaches , joint pain , dizziness , sleep disorders , depression or even hallucinations . Furthermore, it can lead to allergic skin reactions , indigestion or cardiac arrhythmiascome. In particular, the interference with the metabolism of other drugs by inhibiting the cytochrome P450 system has largely pushed cimetidine off the market.

The other H2-receptor antagonists do not interfere with the detoxification process in the liver . However, they also show side effects, which are less common due to the use of smaller amounts. For example, ranitidine or famotidine sometimes develop similar side effects. Allergic skin reactions with itching and rashes can occur. Gastrointestinal problems with nausea , vomiting , diarrhea or constipation are also observed. Finally, in rare cases, headaches and joint pain can also occur. All H2-receptor antagonists are contraindicated in hypersensitivity, pregnancyand during lactation together.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.