Gastric Acid Inhibitors

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Gastric Acid Inhibitors

Recommended dosages
Side effects


Gastric acid inhibitors are medications that reduce the production of stomach acid. They are different from antacids, which act on stomach acid after it has been produced and released into the stomach.


Gastric acid inhibitors are used to treat conditions that are either caused or made worse by the presence of acid in the stomach. These conditions include gastric ulcers; gastroesophageal reflux disease (GERD); and Zollinger-Ellison syndrome, which is marked by atypical gastric ulcers and excessive amounts of stomach acid. Gastric acid inhibitors are also widely used to protect the stomach from drugs or conditions that may cause stomach ulcers. Medications that may cause ulcers include steroid compounds and nonsteroidal anti-inflammatory drugs (NSAIDs), which are often used to treat arthritis. Gastric acid inhibitors offer some protection against the stress ulcers that are associated with some types of illness and with surgery.


There are two types of gastric acid inhibitors, H2-receptor blockers and proton pump inhibitors. H2-receptor blockers are a type of antihistamine. Histamine, in addition to its well-known effects in colds and allergies, also stimulates the stomach to produce more acid. The receptors (nerve endings) that respond to the presence of histamine are called H2 receptors, to distinguish them from the H1 receptors involved in causing allergy symptoms. The most common H2-receptor blockers are cimetidine (Tagamet), famotidine (Pepcid), nizatidine (Axid), and ranitidine (Zantac).

The proton pump inhibitors (PPIs) are drugs that block an enzyme called hydrogen/potassium adenosine triphosphatase in the cells lining the stomach. Blocking this enzyme stops the production of stomach acid. These drugs are more effective in reducing stomach acid than the H2-receptor blockers. The PPIs include such medications as omeprazole (Prilosec), esomeprazole (Nexium), lansoprazole (Prevacid), pantoprazole (Protonix) and rabeprazole (AcipHex).

Recommended dosages

The recommended dosage depends on the specific drug, the purpose for which it is being used, and the route of administration, whether oral or intravenous. Patients should check with the physician who prescribed the medication or the pharmacist who dispensed it. If the drug is an over-the-counter preparation, patients should read the package labeling carefully, and discuss the correct use of the drug with their physician or pharmacist. This precaution is particularly important with regard to the H2-receptor blockers, because they are available in over-the-counter (OTC) formulations as well as prescription strength. The two are not interchangeable; OTC H2-receptor blockers are only half as strong as the lowest available dose of prescription-strength versions of these drugs.

Patients should not use the over-the-counter preparations as an alternative to seeking professional care. For some conditions, particularly stomach ulcers, acid-inhibiting drugs may relieve the symptoms, but will not cure the underlying problems, which require both acid reduction and antibiotic therapy.

Gastric acid inhibitors work best when they are taken regularly, so that the amounts of stomach acid are kept low at all times. Patients should check the package directions or ask the physician or pharmacist for instructions on the best way to take the medicine.


There are relatively few adverse reactions when gastric acid inhibitors are used for one to two doses before or just after surgery, The side effects listed below are most often seen with long-term use.


Enzyme— A biological compound that causes changes in other compounds.

Gastroesophageal reflux disease (GERD)— A condition in which the contents of the stomach flow backward into the esophagus. There is no known single cause.

Nonsteroidal anti-inflammatory drugs (NSAIDs)— Drugs that relieve pain and reduce inflammation but are not related chemically to cortisone. Common drugs in this class are aspirin, ibuprofen (Advil, Motrin), naproxen (Aleve, Naprosyn), ketoprofen (Orudis), and several others.

Platelets— Disk-shaped structures found in blood that play an active role in blood clotting. Platelets are also known as thrombocytes.

Receptor— A sensory nerve ending that responds to chemical or other stimuli of various kinds.

Stress ulcers— Stomach ulcers that occur in connection with some types of physical injury, including burns and invasive surgical procedures.

Thrombocytopenia— A disorder characterized by a drop in the number of platelets in the blood.

Zollinger-Ellison syndrome A condition marked by stomach ulcers, with excess secretion of stomach acid and tumors of the pancreas.

H2-receptor blockers

Although the H2-receptor blockers are very safe drugs, they are capable of causing thrombocytopenia, a disorder in which there are too few platelets in the blood. This deficiency may cause bleeding problems, since platelets are essential for blood clotting. Platelet deficiencies can only be recognized by blood tests; there are no symptoms that the patient can see or feel. In addition to affecting platelet levels, the H2-receptor blockers may cause changes in heart rate, making the heart beat either faster or slower than normal. Patients should call a physician immediately if any of these signs occur:

  • tingling of the fingers or toes;
  • difficulty breathing;
  • difficulty swallowing;
  • swelling of the face or lips;
  • rapid heartbeat; or
  • slow heartbeat.

In addition to these signs, the H2-receptor blockers may cause the following unwanted reactions:

  • headache;
  • diarrhea;
  • dizziness;
  • drowsiness;
  • nausea;
  • depression;
  • skin rash; or
  • vomiting.

In addition, cimetidine is an inhibitor of male sex hormones; it may cause loss of libido, breast tenderness and enlargement, and impotence.

Ranitidine may cause loss of hair or severe skin rashes that require prompt medical attention. In rare cases, this drug may cause a reduction in the white blood cell count.

Before using H2-receptor blockers, people with any of these medical problems should make sure their physicians are aware of their conditions:

  • kidney disease;
  • liver disease; or
  • medical conditions associated with confusion or dizziness.

Proton pump inhibitors

The proton pump inhibitors are also very safe, but have been associated with rare but severe skin reactions. Patients should be sure to report any rash or change in the appearance of the skin when taking these drugs. The following adverse reactions are also possible:

  • stomach cramps;
  • weakness;
  • chest pain;
  • constipation;
  • diarrhea;
  • dizziness;
  • drowsiness;
  • gas pains;
  • headache;
  • nausea with or without vomiting;
  • itching; and
  • blood in urine.

The PPIs make some people feel drowsy, dizzy, lightheaded, or less alert. Anyone who takes these drugs should not drive, use heavy machinery, or do anything else that requires full alertness until they have found out how the drugs affect them.

Before using proton pump inhibitors, people with liver disease should make sure their physicians are aware of their condition.

Taking gastric acid reducers with certain other drugs may affect the way the drugs work or may increase the chance of side effects.

Side effects

The most common side effects of both types of gastric acid reducer are mild diarrhea, nausea, vomiting, stomach or abdominal pain, dizziness, drowsiness, lightheadedness, nervousness, sleep problems, and headache. The frequency of each type of problem varies with the specific drug selected and the dose. These problems usually go away as the body adjusts to the drug and do not require medical treatment unless they are bothersome.

Serious side effects are uncommon with these medications, but may occur. Patients should consult a physician immediately if they notice any of the following:

  • skin rash or such other skin problems as itching, peeling, hives, or redness;
  • fever;
  • agitation or confusion;
  • hallucinations;
  • shakiness or tremors;
  • seizures or convulsions;
  • tingling in the fingers or toes;
  • pain at the injection site that lasts for some time after the injection;
  • pain in the calves that spreads to the heels;
  • swelling of the calves or lower legs;
  • swelling of the face or neck;
  • difficulty swallowing;
  • rapid heartbeat;
  • shortness of breath; or
  • loss of consciousness.

Other side effects may occur in rare instances. Anyone who has unusual symptoms after taking gastric acid inhibitors should get in touch with his or herphysician.


Gastric acid inhibitors may interact with other medicines. When an interaction occurs, the effects of one or both of the drugs may change or the risk of side effects may be increased. Anyone who takes gastric acid inhibitors should give their physician a list of all the other medicines that he or she is taking.

Of the drugs in this class, cimetidine has the highest number of drug interactions, and specialized reference works should be consulted for guidance about this medication.

The drugs that may interact with H2-receptor blockers include:

  • itraconazole (Sporanox);
  • ketoconazole (Nizoral);
  • warfarin (Coumadin);
  • dofetilide (Tikosyn); and
  • drugs given to open the airway (bronchodilators), including aminophylline, theophylline (Theo-Dur and other brands), and oxtriphylline (Choledyl and other brands).

Drugs that may interact with proton pump inhibitors include:

  • itraconazole (Sporanox);
  • ketoconazole (Nizoral);
  • phenytoin (Dilantin) and other anticonvulsant drugs;
  • cilostazol (Pletal); and
  • voriconazole (Vfend).

The preceding lists do not include every drug that may interact with gastric acid inhibitors. Patients should consult a physician or pharmacist before combining gastric acid inhibitors with any other prescription or nonprescription (over-the-counter) medicine.



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“Esomeprazole.” Medline Plus. January 1, 2008. (March 31, 2008).

“Ranitidine.” Medline Plus. July 1, 2003. (March 31, 2008).


American Society for Gastrointestinal Endoscopy, 1520 Kensington Road, Suite 202, Oak Brook, IL, 60523, (630) 573-0600,

American Society of Health-System Pharmacists, 7272 Wisconsin Avenue, Bethesda, MD, 20814, (301) 657-3000,

Society for Gastroenterology Nurses and Associates, 401 North Michigan Avenue, Chicago, IL, 60611-4267,(800) 245-7462,

U.S. Food and Drug Administration, 5600 Fishers Lane, Rockville, MD, 20857-0001, (888) INFO-FDA,

Samuel Uretsky, Pharm.D.

Laura Jean Cataldo, R.N., Ed.D.