An antacid is a substance which
neutralizes stomach acidity and is used to relieve
heartburn
Heartburn is a burning sensation felt behind the breastbone. It is a symptom that is commonly linked to acid reflux and is often triggered by food, particularly fatty, sugary, spicy, chocolate, citrus, onion-based and tomato-based products. Ly ...
,
indigestion, or an upset stomach.
Some antacids have been used in the treatment of
constipation and
diarrhea.
Marketed antacids contain
salts of
aluminum
Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
,
calcium,
magnesium
Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
, or
sodium
Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
.
Some preparations contain a combination of two
salts, such as
magnesium carbonate and
aluminum hydroxide (e.g.,
hydrotalcite).
Medical uses
Antacids are available
over the counter and are taken by mouth to quickly relieve occasional
heartburn
Heartburn is a burning sensation felt behind the breastbone. It is a symptom that is commonly linked to acid reflux and is often triggered by food, particularly fatty, sugary, spicy, chocolate, citrus, onion-based and tomato-based products. Ly ...
, the major symptom of
gastroesophageal reflux disease and
indigestion. Treatment with antacids alone is
symptomatic and only justified for minor symptoms.
Alternative uses for antacids include constipation, diarrhea, hyperphosphatemia, and urinary alkalization.
Some antacids are also used as an
adjunct to pancreatic enzyme replacement therapy in the treatment of
pancreatic insufficiency.
Non-particulate antacids (
sodium citrate) increase gastric
pH with little or no effect on gastric volume, and therefore may see some limited use in pre-operative procedures. Sodium citrate should be given within one hour of surgery to be the most effective.
Side effects
Conventional effervescent tablets contain a significant amount of
sodium
Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
and are associated with increased odds of adverse cardiovascular events according to a 2013 study. Alternative sodium-free formulations containing
magnesium salts may cause diarrhea, whereas those containing
calcium or
aluminum
Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
may cause
constipation.
Long-term use of antacids containing
aluminum
Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
may increase the risk of developing
osteoporosis.
In vitro
''In vitro'' (meaning ''in glass'', or ''in the glass'') Research, studies are performed with Cell (biology), cells or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in ...
studies have found a potential for acid rebound to occur due to antacid overuse, however the significance of this finding has been called into question.
Properties of antacids
When an excess amount of acid is produced in the
stomach
The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...
, the natural
mucous barrier that protects the lining of the stomach can degrade, leading to
pain
Pain is a distressing feeling often caused by intense or damaging Stimulus (physiology), stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sense, sensory and emotional experience associated with, or res ...
and
irritation. There is also potential for the development of
acid reflux, which can cause pain and damage to the
esophagus
The esophagus (American English), oesophagus (British English), or œsophagus (Œ, archaic spelling) (American and British English spelling differences#ae and oe, see spelling difference) all ; : ((o)e)(œ)sophagi or ((o)e)(œ)sophaguses), c ...
. Antacids contain
alkaline
In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The ...
ions that
chemically neutralize stomach
gastric acid, reducing damage to the stomach lining and
esophagus
The esophagus (American English), oesophagus (British English), or œsophagus (Œ, archaic spelling) (American and British English spelling differences#ae and oe, see spelling difference) all ; : ((o)e)(œ)sophagi or ((o)e)(œ)sophaguses), c ...
, and relieving pain.
Some antacids also inhibit
pepsin, an
enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
that can damage the
esophagus
The esophagus (American English), oesophagus (British English), or œsophagus (Œ, archaic spelling) (American and British English spelling differences#ae and oe, see spelling difference) all ; : ((o)e)(œ)sophagi or ((o)e)(œ)sophaguses), c ...
in
acid reflux.
Antacids do not directly inhibit acid
secretion
Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classical mec ...
, and thus are distinct from acid-reducing drugs like
H2-receptor antagonists or
proton pump inhibitors.
Antacids do not kill the bacterium, ''
Helicobacter pylori'', which causes most
ulcers.
Types
Antacids are mainly classified into two categories:
* Systemic (absorbable) antacids: They are
water soluble and systemically absorbed and pass into the
bloodstream. e.g.
sodium bicarbonate or
sodium citrate
* Non-systemic (non-absorbable) antacids: They are
insoluble and not absorbed into systemic circulation. They only act in the
stomach
The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...
e.g.
magnesium carbonate or
calcium carbonate
Interactions

Antacids are known to
interact with several
oral medications, including
fluoroquinolone and
tetracycline antibiotic
An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...
s,
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
,
itraconazole, and
prednisone
Prednisone is a glucocorticoid medication mostly used to immunosuppressive drug, suppress the immune system and decrease inflammation in conditions such as asthma, COPD, and rheumatologic diseases. It is also used to treat high blood calcium ...
.
Metal
chelation is responsible for some of these interactions (e.g.
fluoroquinolones,
tetracyclines), leading to decreased absorption of the chelated drug. Some interactions may be due to the
pH increase observed in the
stomach
The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...
following antacid
ingestion, leading to increased absorption of weak acids, and decreased absorption of weak bases. Antacids also cause an increase in
pH of the
urine
Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...
(alkalization), which may cause increased
blood concentrations of weak bases, and increased
excretion
Excretion is elimination of metabolic waste, which is an essential process in all organisms. In vertebrates, this is primarily carried out by the lungs, Kidney (vertebrates), kidneys, and skin. This is in contrast with secretion, where the substa ...
of weak acids.
A proposed method to mitigate the effects of
stomach
The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...
acidity and
chelation on drug absorption is to space out the administration of antacids with interacting
medication
Medication (also called medicament, medicine, pharmaceutical drug, medicinal product, medicinal drug or simply drug) is a drug used to medical diagnosis, diagnose, cure, treat, or preventive medicine, prevent disease. Drug therapy (pharmaco ...
s by at least two hours, however this method has not been well studied for drugs affected by
urine alkalization.
There are concerns regarding interactions between delayed-release tablets and antacids, as antacids may increase the stomach
pH to a point at which the coating of the delayed-release tablet will dissolve, leading to degradation of the drug if it is
pH sensitive.
Formulations
Antacids may be formulated with other
active ingredients such as
simethicone
Simeticone (International Nonproprietary Name, INN), also known as simethicone (United States Adopted Name, USAN), is an anti-foaming agent used to reduce bloating, discomfort or pain caused by excessive gas.
Medical uses
Simeticone is used to ...
to control
gas, or
alginic acid to act as a physical barrier to acid.
Liquids
Several liquid antacid preparations are
marketed. Common liquid preparations include
milk of magnesia and magnesium/aluminum
combinations. A potential advantage of using a liquid preparation over a tablet is that liquids may provide quicker relief, however this may coincide with a shorter duration of action.
Tablets
Chewable tablets
Chewable tablets are one of the most common forms of antacids, most frequently made from
carbonate
A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...
or
hydroxide salts, and are readily available over the counter. Upon reaching the
stomach
The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...
, the powdered antacid salts bind to
hydronium (H
+) ions, producing
chloride salts, carbon dioxide, and water. This process reduces the concentration of H
+ ions in the stomach, raising the pH and neutralizing the acid.
Common carbonate salts available in tablet form include those of calcium, magnesium, aluminum, and sodium.
Some common American brands are
Tums, Gaviscon chewable tablets, and
Maalox chewable tablets.
Effervescent tablets
Effervescent tablets are tablets which are designed to dissolve in
water
Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
, and then release
carbon dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
. Common ingredients include
citric acid and
sodium bicarbonate, which react when in contact with water to produce
carbon dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
. Effervescent antacids may also contain
aspirin,
sodium carbonate, or
tartaric acid.
Those containing aspirin may cause further
gastric irritation and
ulceration
An ulcer is a discontinuity or break in a bodily membrane that impedes normal function of the affected Organ (biology), organ. According to Robbins's pathology, "ulcer is the breach of the continuity of skin, epithelium or mucous membrane caus ...
due to
aspirin's effects on the
mucous membrane of the
stomach
The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...
.
Brand names
Some
brand
A brand is a name, term, design, symbol or any other feature that distinguishes one seller's goods or service from those of other sellers. Brands are used in business, marketing, and advertising for recognition and, importantly, to create and ...
s include
Alka-Seltzer, Gaviscon,
Tums, Gelusil and
Eno.
References
External links
*
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