Antacids and Their Pharmacology

Study Notes

Antacids are a class of medications that neutralize stomach acid.
They are available over the counter (OTC) and are often used in combination with other drugs.
Common examples include magnesium hydroxide, aluminum hydroxide, simethicone, magaldrate, calcium carbonate, and sodium bicarbonate.

Antacids neutralize gastric acid.
They are distributed throughout the gastrointestinal (GI) tract and are primarily eliminated in the feces.

Antacids reduce the total amount of acid in the GI tract, giving peptic ulcers time to heal.

Used to relieve pain and promote healing in peptic ulcer disease (PUD).
Relieve symptoms of acid indigestion, heartburn, dyspepsia, and gastroesophageal reflux disease (GERD).

Antacids can interfere with the absorption of oral medications if taken concurrently.
Absorption of digoxin, iron salts, isoniazid, quinolones, and tetracyclines may be reduced if taken within two hours of antacids.

Commonly known as H2 blockers, they inhibit the action of histamine on parietal cells in the stomach.
Examples include cimetidine, nizatidine, ranitidine, and famotidine.

Cimetidine, nizatidine, and ranitidine are rapidly and completely absorbed from the GI tract.
Famotidine is not completely absorbed.
Food and antacids can reduce absorption.
Distributed throughout the body, metabolized by the liver, and excreted in the urine.

Block histamine from stimulating acid-secreting parietal cells, reducing gastric acid secretion.
Promote healing of ulcers by eliminating their cause.

Treatment of active duodenal ulcers or benign gastric ulcers.
Treatment of pathologic GI hypersecretory conditions such as Zollinger-Ellison syndrome.
Reduce gastric acid production and prevent stress ulcers in severely ill patients and those with reflux esophagitis or upper GI bleeding.
Treatment of erosive gastroesophageal reflux.
Relief of symptoms like heartburn, acid indigestion, and sour stomach.

Antacids reduce the absorption of cimetidine, nizatidine, and famotidine.
Cimetidine can increase the blood levels of oral anticoagulants, propranolol, benzodiazepines, tricyclic antidepressants (TCAs), theophylline, procainamide, quinidine, lidocaine, phenytoin, calcium channel blockers, cyclosporine, carbamazepine, and narcotic analgesics by inhibiting their metabolism in the liver.
Cimetidine inhibits the metabolism of ethyl alcohol in the stomach, leading to higher blood alcohol levels.

Headache, dizziness, malaise, muscle pain, nausea, diarrhea/constipation, rashes, itching, loss of sexual desire, and impotence.
Famotidine and nizatidine have fewer adverse reactions, with headache being the most common followed by constipation/diarrhea and rash.

PPIs disrupt the chemical binding in stomach cells, reducing acid production and promoting ulcer healing.
Examples include rabeprazole, pantoprazole, omeprazole, lansoprazole, and esomeprazole.

Administered orally in enteric-coated formulas to bypass the stomach due to their acid sensitivity.
They are dissolved in the small intestine, where absorption is rapid.
Highly protein-bound and extensively metabolized by the liver to inactive compounds, then eliminated in the urine.

Block the final step in gastric acid secretion by combining with hydrogen, potassium, and adenosine triphosphate in parietal cells.

Short-term treatment of active gastric ulcers, active duodenal ulcers, erosive esophagitis, symptomatic GERD unresponsive to other therapies, and active peptic ulcers associated with H. pylori infection (in combination with antibiotics).
Long-term treatment of hypersecretory states like Zollinger-Ellison syndrome.

Interfere with the metabolism of diazepam, phenytoin, and warfarin, leading to increased half-lives and elevated plasma concentrations of these drugs.

Common CNS effects include dizziness and headache.
GI effects include abdominal pain, diarrhea, nausea/vomiting, dry mouth, and tongue atrophy.
Upper respiratory tract (URT) symptoms include cough and stuffy nose.