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 Indigestion, also known as dyspepsia or upset stomach, is a condition of impaired digestion. Symptoms may include upper abdominal fullness, heartburn, nausea, belching, or upper abdominal pain. People may also experience feeling full earlier ...

, or an upset stomach. Some antacids have been used in the treatment of

constipation Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The Human feces, stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the ...

and

diarrhea Diarrhea (American English), also spelled diarrhoea or diarrhœa (British English), is the condition of having at least three loose, liquid, or watery bowel movements in a day. It often lasts for a few days and can result in dehydration d ...

. Marketed antacids contain

salts In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...

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 Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

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

, 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

, the major symptom of

gastroesophageal reflux disease Gastroesophageal reflux disease (GERD) or gastro-oesophageal reflux disease (GORD) is a chronic upper gastrointestinal disease in which stomach content persistently and regularly flows up into the esophagus, resulting in symptoms and/or ...

and

. 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

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

may cause

. Long-term use of antacids containing

may increase the risk of developing

osteoporosis Osteoporosis is a systemic skeletal disorder characterized by low bone mass, micro-architectural deterioration of bone tissue leading to more porous bone, and consequent increase in Bone fracture, fracture risk. It is the most common reason f ...

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 Gastric acid or stomach acid is the acidic component – hydrochloric acid – of gastric juice, produced by parietal cells in the gastric glands of the stomach lining. In humans, the pH is between one and three, much lower than most other a ...

, reducing damage to the stomach lining and

, and relieving pain. Some antacids also inhibit

pepsin Pepsin is an endopeptidase that breaks down proteins into smaller peptides and amino acids. It is one of the main digestive enzymes in the digestive systems of humans and many other animals, where it helps digest the proteins in food. Pe ...

, 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

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 inhibitor Proton-pump inhibitors (PPIs) are a class of medications that cause a profound and prolonged reduction of stomach acid production. They do so by irreversibly inhibiting the stomach's H+/K+ ATPase proton pump. The body eventually synthesizes ne ...

s. Antacids do not kill the bacterium, ''

Helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, Flagellum#bacterial, flagellated, Bacterial cellular morphologies#Helical, helical bacterium. Mutants can have a rod or curved rod shape that exhibits l ...

'', which causes most

ulcers An ulcer is a discontinuity or break in a bodily membrane that impedes normal function of the affected organ. According to Robbins's pathology, "ulcer is the breach of the continuity of skin, epithelium or mucous membrane caused by sloughing ...

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 Sodium bicarbonate ( IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda (or simply “bicarb” especially in the UK) is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cat ...

or sodium citrate * Non-systemic (non-absorbable) antacids: They are insoluble and not absorbed into systemic circulation. They only act in the

e.g. magnesium carbonate or

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

Interactions

Basic structure of tetracycline chelating a metal

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 ...

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 Itraconazole, sometimes abbreviated ITZ, is an antifungal medication used to treat a number of fungal infections. This includes aspergillosis, blastomycosis, coccidioidomycosis, histoplasmosis, and paracoccidioidomycosis. It may be given ...

, 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 Chelation () is a type of bonding of ions and their molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These l ...

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

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 Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood is com ...

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

acidity and

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

combination In mathematics, a combination is a selection of items from a set that has distinct members, such that the order of selection does not matter (unlike permutations). For example, given three fruits, say an apple, an orange and a pear, there are ...

s. 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 ...

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It ...

, and are readily available over the counter. Upon reaching the

, the powdered antacid salts bind to

hydronium In chemistry, hydronium (hydroxonium in traditional British English) is the cation , also written as , the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid is dissolved ...

(H⁺) ions, producing

chloride The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pr ...

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 Citric acid is an organic compound with the formula . It is a Transparency and translucency, colorless Weak acid, weak organic acid. It occurs naturally in Citrus, citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, ...

and

, which react when in contact with water to produce

. Effervescent antacids may also contain

aspirin Aspirin () is the genericized trademark for acetylsalicylic acid (ASA), a nonsteroidal anti-inflammatory drug (NSAID) used to reduce pain, fever, and inflammation, and as an antithrombotic. Specific inflammatory conditions that aspirin is ...

sodium carbonate Sodium carbonate (also known as washing soda, soda ash, sal soda, and soda crystals) is the inorganic compound with the formula and its various hydrates. All forms are white, odourless, water-soluble salts that yield alkaline solutions in water ...

, 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

's effects on the mucous membrane of the

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

* {{Authority control