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Antacids

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What are antacids, and how do they work?

Antacids are a class of drugs used to treat conditions caused by the acid that is produced by the stomach. The stomach naturally secretes an acid called hydrochloric acid that helps to break down proteins. This acid causes the contents of the stomach to be acidic in nature, with a pH level of 2 or 3 when acid secretion is active. (pH levels are a measure of acidity in the stomach: the lower the number, the greater the acidity.) The stomach, duodenum, and esophagus are protected from acid by several protective mechanisms. When there is too much acid or protective mechanisms are inadequate, the lining of the stomach, duodenum or esophagus may become damaged by the acid, giving rise to inflammation and ulcerations and their various gastrointestinal symptoms such as nausea, abdominal pain, and heartburn (due to gastroesophageal reflux disease or GERD).

Antacids reduce acidity by neutralizing (counteracting) acid, reducing the acidity in the stomach, and reducing the amount of acid that is refluxed into the esophagus or emptied into the duodenum. Antacids also work by inhibiting the activity of pepsin, a digestive enzyme produced in the stomach that is active only in an acid environment and, like acid, is believed to be injurious to the lining of the stomach, duodenum, and esophagus.

It is important to note that when antacids are taken on an empty stomach they provide acid reduction for 20 to 40 minutes only because the antacid is rapidly emptied into the duodenum. When taken after a meal, (approximately 1 hour afterwards) antacids reduce acid for at least three hours since food from the meal slows emptying of the antacid (and food) from the stomach. It is important to discuss the use of antacids with a physician or pharmacist, especially if used in combination with other prescribed medications so as to avoid drug interactions.

For what conditions are antacids used?

Antacids are used commonly for symptoms such as heartburn, abdominal pain (sometimes described as sour stomach) and nausea resulting from a number of conditions such as, inflammation or acid-peptic ulcers of the esophagus (esophagitis), stomach (gastritis), and duodenum (duodenitis)

Aluminum carbonate antacids can be used to treat and manage hyperphosphatemia (abnormally elevated levels of phosphate in the blood) since they bind phosphate in the intestine and prevent it from being absorbed into the body. Because of this ability to bind phosphate in the intestine, aluminum carbonate antacids also can be used with a low phosphate diet to prevent the formation of kidney stones, since kidney stones are made up of various elements including phosphates.

Calcium carbonate antacids are used in conditions of calcium deficiency such as postmenopausal osteoporosis since some of the calcium is absorbed into the body.

Magnesium oxide antacids are used to treat magnesium deficiencies from either diets or medications that cause magnesium depletion.

Off label (not FDA-approved) uses for antacids containing aluminum and magnesium or aluminum alone include preventing bleeding from stress-induced ulcers. Other off-label uses for antacids are treatment and maintenance of healing of duodenal ulcers and treatment of gastric ulcers.

Are there any differences among the different types of antacids?

Some antacid products may neutralize more acid in the stomach than others. The way to express the ability of an antacid to neutralize acid is by determining the antacid's neutralizing capacity (ANC). The ANC is expressed as milliequivalents (mEq) of acid that is neutralized, and it measures the ability of the antacid to neutralize acids (to a ph of 3.5 to 4). Per FDA requirements, an antacid must have a neutralizing capacity of ≥5 mEq per dose. The most effective antacids should have a high acid neutralization capacity and rapid gastric acid neutralization qualities. Antacids such as sodium bicarbonate and calcium carbonate have the greatest neutralizing capacity but are not used for long periods of time due to adverse events. (Please see the sections on warnings/precautions and side effects.)

An antacid's onset of neutralizing action (how fast the drug dissolves in gastric acid) varies among different antacids. Sodium bicarbonate and magnesium hydroxide dissolve quickly and provide a rapid buffering effect, while aluminum hydroxide and calcium carbonate dissolve slowly. Antacid suspensions generally dissolve more easily than tablets or powders. If a tablet antacid is used, however, it is advisable to chew the tablets thoroughly for maximal effectiveness.

Another difference amongst the antacids is the duration of action (how long it continues to neutralize acid in the stomach). Sodium bicarbonate and magnesium hydroxide have the shortest duration of neutralizing action, while aluminum hydroxide and calcium carbonate have the longest. Combination aluminum magnesium antacids have an intermediate duration of action.

What are the warnings and precautions for antacids?

  • Antacids (for example, calcium carbonate) when consumed in high doses and for long periods of time may cause acid rebound. Acid rebound is a condition in which the stomach produces even more acid after the consumption of foods and drinks. Fortunately, the effects of acid rebound are not clinically important.
  • High-dose calcium carbonate and sodium bicarbonate when taken together can cause a condition called milk-alkali syndrome. Its symptoms include headache, nausea, irritability, and weakness, hypercalcemia (high blood calcium levels), and reduced function of the kidneys.
  • Extensive use of aluminum-containing antacids may cause hypophosphatemia (low phosphate levels in the blood), which in severe cases could lead to muscle weakness, anorexia, and osteomalacia (softening of the bones due to defective bone mineralization).
  • Antacids containing aluminum hydroxide should be used with caution in patients who have recently suffered massive upper gastrointestinal bleeding.
  • For patients with conditions such as high blood pressure, chronic heart failure, renal failure and those who have sodium or salt-restricted diets, it is important to pay attention to the sodium level in sodium-based antacid preparations such as sodium bicarbonate
  • Antacids should not be given to children under six years of age.

What are the side effects of antacids?

  • Antacids may cause dose-dependent rebound hyperacidity and milk-alkali syndrome.
  • Antacids that contain aluminum hydroxide may cause constipation, aluminum-intoxication, osteomalacia, and hypophosphatemia.
  • Antacids that contain magnesium have a laxative effect that may cause diarrhea, and in patients with renal failure they may cause increased magnesium levels in the blood, because of the reduced ability of the kidneys to eliminate magnesium from the body in the urine.

With which drugs do antacids interact?

When antacids are taken with acidic drugs (for example, digoxin [Digitek], phenytoin [Dilantin], chlorpromazine [Thorazine], [isoniazid]), they cause the absorption of the acidic drugs to be decreased, which causes low blood concentrations of the drugs, which ultimately results in reduced effects of the drugs.

Antacids taken with drugs such as pseudoephedrine (Sudafed, Semprex D, Clarinex-D 12hr, Clarinex-D 24hr, , Deconsal, Entex PSE, Claritin D, and more), and levodopa (Dopar), increase absorption of the drugs and can cause toxicity/adverse events due to increased blood levels of the drugs.

Antacids that contain magnesium trisilicate and magnesium hydroxide when taken with some other medications (such as tetracycline) will bind to the drugs, and reduce their absorption and effects.

Sodium bicarbonate has a strong effect on the acidity of the urine, and this can affect the elimination (excretion) of some drugs by the kidney. Thus, sodium bicarbonate inhibits the excretion of basic drugs such as quinidine (Quinidex, Quinidine Gluconate, Quinidine Sulfate, Quinidine Injection) and amphetamines, and increases the excretion of acidic drugs such as aspirin.

What antacids are available?

  • AlternaGEL (liquid)
  • Aluminum Hydroxide
  • Aluminum Hydroxide Gel (suspension)
  • Aluminum-magnesium hydroxide sulfate (Magaldrate)
  • Amphojel (tablets)
  • Calcium acetate (PhosLo tablets)
  • Calcium carbonate
  • Citra pH (solution)
  • Concentrated Aluminum Hydroxide Gel (suspension)
  • Concentrated Aluminum Hydroxide Gel (liquid)
  • Concentrated Phillips' Milk of Magnesia (liquid)
  • Dialume (capsules)
  • Dulcolax (Liquid)
  • Isopan (Liquid)
  • Mag-Ox 400 (tablets)
  • Magnesium Hydroxide
  • Magnesium Oxide
  • Magnesium Oxide (tablets)
  • Magaldrate (liquid)
  • Maox 420 (tablets)
  • Milk of Magnesia (liquid)
  • Phillips' Chewable (tablets, chewable)
  • Uro-Mag (capsules)
  • Riopan (suspension)
  • Sodium Bicarbonate
  • Sodium Citrate

Antacid combinations

  • Alka-Seltzer Effervescent Tablets,
  • Alamag Suspension,
  • Bromo Seltzer Effervescent Granules
  • Gaviscon Extra Strength Antacid,
  • Gaviscon Liquid,
  • Gas-X with Maalox Extra Strength Tablets,
  • Maalox Regular Strength Liquid,
  • Mylanta Antacid Gelcaps,
  • Rolaids Tablets, and
  • Titralac Extra Strength Tablets, etc.

Reviewed by:
Tova Alladice, M.D.
American Board of Physical Medicine & Rehabilitation

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