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THE MERCK MANUAL MEDICAL LIBRARY: The Merck Manual of Medical Information--Home Edition
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Antacids

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Heartburn, indigestion, and sour stomach are a few of the many terms used to describe digestive upset. Self-diagnosis of indigestion is risky because its causes vary from a minor dietary indiscretion to peptic ulcer disease or even stomach cancer. Sometimes symptoms of heart disease resemble acute indigestion. If symptoms last longer than 2 weeks, people should see their doctor.

The goal of treatment for indigestion is to prevent the production of stomach acid or to neutralize the acid. Histamine-2 (H2) blockers, including cimetidine Some Trade Names
TAGAMET
, famotidine Some Trade Names
PEPCID
, nizatidine Some Trade Names
AXID
, and ranitidine Some Trade Names
ZANTAC
, help prevent heartburn by reducing the amount of acid produced in the stomach. Antacids neutralize stomach acid. Although antacids cannot completely neutralize stomach acid, they can raise the pH level in the stomach from 2 (very acidic) to between 3 and 4. This increase neutralizes almost 99% of stomach acid and significantly relieves symptoms for most people. Antacids provide relief more quickly than H2 blockers, but H2 blockers provide longer-lasting relief.

Most antacid products contain one or more of four active ingredients: aluminum salts, magnesium salts, calcium carbonate Some Trade Names
TUMS
CALTRATE
OSCAL
, and sodium bicarbonate. All products provide relief in a minute or less, but products vary in how long they provide relief—from only about 10 minutes to more than an hour and a half.

Antacids can interact with many different prescription drugs, so a pharmacist should be consulted about possible drug-drug interactions before antacids are taken. Anyone who has heart disease, high blood pressure, or a kidney disorder should consult a doctor before selecting an antacid. The H2 blocker cimetidine Some Trade Names
TAGAMET
may also interact with some prescription drugs. Therefore, its use should be monitored by a doctor or pharmacist.

Aluminum and Magnesium

Antacids that contain both aluminum and magnesium salts once seemed ideal because one ingredient complemented the other. Aluminum salts, which dissolve slowly in the stomach, start to work gradually but provide long-lasting relief. They also cause constipation. Magnesium salts act fast and neutralize acids effectively. They can also act as a laxative. Antacids containing both ingredients should provide quick, long-lasting relief with less risk of diarrhea or constipation. However, the long-term safety of antacids containing aluminum has been questioned. Prolonged use may weaken bones by depleting the body of phosphorus and calcium.

Calcium Carbonate

Calcium carbonate Some Trade Names
TUMS
CALTRATE
OSCAL
, or chalk, has been a mainstay of antacids for a long time. Calcium carbonate Some Trade Names
TUMS
CALTRATE
OSCAL
acts fast and neutralizes acids for a relatively long time. Also, it is an inexpensive source of calcium; amounts range from 500 to 1000 milligrams per tablet or dose. However, people can overdose on calcium (see Minerals and Electrolytes: Calcium). The maximum daily amount should not exceed 2000 milligrams unless a doctor has directed otherwise.

Sodium Bicarbonate

One of the least expensive and most readily available antacids is no farther away than the kitchen cabinet. Sodium bicarbonate, or baking soda, neutralizes acid quickly. The baking soda burp is a sign that this antacid is working; the burp is caused by release of carbon dioxide gas, which occurs when the antacid neutralizes the acid.

Although sodium bicarbonate may provide a short-term solution to indigestion, too much bicarbonate can wreak havoc with the body's acid-base balance and lead to metabolic alkalosis (see Acid-Base Balance: Alkalosis). The high sodium content may also cause problems for people with heart failure or high blood pressure.

Last full review/revision February 2003

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