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, H 2 -receptor blockers and proton pump inhibitors. H 2 -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 H 2 receptors, to distinguish them from the H 1 receptors involved in causing allergy symptoms. The most common H 2 -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 H 2 -receptor blockers. The PPIs include such medications as omeprazole (Prilosec), esomeprazole (Nexium), lansoprazole (Prevacid), pantoprazole (Protonix) and rabeprazole (AcipHex).
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 H 2 -receptor blockers, because they are available in over-thecounter (OTC) formulations as well as prescription strength. The two are not interchangeable; OTC H 2 -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.
Although the H 2 -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 H 2 -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:
In addition to these signs, the H 2 -receptor blockers may cause the following unwanted reactions:
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 H 2 -receptor blockers, people with any of these medical problems should make sure their physicians are aware of their conditions:
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:
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.
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:
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 her physician.
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 H 2 -receptor blockers include:
Drugs that may interact with proton pump inhibitors include:
The preceding lists do not include every drug that may interact with gastric acid inhibitors. Patients should be careful to consult a physician or pharmacist before combining gastric acid inhibitors with any other prescription or nonprescription (over-the-counter) medicine.
"Factors Affecting Drug Response: Drug Interactions." Section 22, Chapter 301 in The Merck Manual of Diagnosis and Therapy , edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 1999.
"Peptic Ulcer Disease." Section 3, Chapter 23 in The Merck Manual of Diagnosis and Therapy , edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 1999.
Reynolds, J. E. F., ed. Martindale: The Extra Pharmacopoeia , 31st ed. London, UK: The Pharmaceutical Press, 1996.
Wilson, Billie Ann, RN, PhD, Carolyn L. Stang, PharmD, and Margaret T. Shannon, RN, PhD. Nurses Drug Guide 2000 . Stamford, CT: Appleton and Lange, 1999.
American Society of Health-System Pharmacists (ASHP). 7272 Wisconsin Avenue, Bethesda, MD 20814. (301) 657-3000. http://www.ashp.org .
United States Food and Drug Administration (FDA). 5600 Fishers Lane, Rockville, MD 20857-0001. (888) INFO-FDA. http://www.fda.gov .
Samuel Uretsky, PharmD