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Although famotidine and ranitidine are distinct molecules, they have the same basic action in the body. They reduce acid production by the cells that line the stomach, by interfering with specific receptors on the outside of stomach cells. Both drugs are suitable for stomach ulcer treatments, gastroesophageal acid reflux disease (GERD) and other conditions that cause an overproduction of stomach acid, but the amounts necessary and the way in which the drugs are absorbed by the body are different.
Famotidine and ranitidine are part of a group of drugs called histamine H2-receptor antagonists. The other two main members, as of 2011, are cimetidine and nizatidine. All of these drugs specifically act on a molecule called a H2-receptor, which sticks out from the outside of some cells.
Inside the stomach, cells with H2-receptors on the outside, called parietal cells, are those cells that produce acid into the stomach area when signals from elsewhere tell them more acid is necessary. Histamine is the particular signal molecule in this case, and famotidine and ranitidine block the H2-receptors from recognizing histamine. This mode of action gives the group of drugs their name, histamine H2- antagonists.
Even though famotidine and ranitidine are completely different molecules, their action is the same. They block the receptor and prevent more acid being produced, which gives them both potential uses in diseases that involve high levels of stomach acid. Examples include GERD and esophagitis, which can cause acid damage to the cells of the digestive system. Ulcers of the stomach and the nearby duodenum can also resolve with histamine H2-receptor antagonist treatment. Cancers of the region that create too much acid production can also be alleviated with one of these drugs.
Products containing famotidine typically need to contain less active ingredient than ranitidine products, with a typical dose of about 40 mg compared to a ranitidine dose of 150 mg. Conversely, more ranitidine is absorbed through the digestive tract than famotidine, but it can take longer to work than famotidine. As a molecule, famotidine has the chemical formula of C8H15N7O2S3, whereas ranitidine has the general formula C13H22N4O3S, and a hydrogen and chlorine atom can be tacked on to make a hydrochloride salt form. The two molecules are different in structure, shape and mass, but still work in the same way on the H2-receptor. People who take one of these drugs for a particular condition do not generally take the other at the same time.