Pharmacology of Antacids
Antacids treat indigestion, heartburn, and acid
reflux. Antacids reduce gastric acid and relieve discomfort. Over-the-counter
(OTC) antacids have dosage forms such as tablets, capsules,
liquids, and chewable tablets and are easily available.
Systemic Antacids
These antacids can enter the
blood circulation and have physiological effects beyond the gastrointestinal
tract. Systemic hyperacidity and metabolic alkalosis are often treated with
these drugs. Examples include:
Sodium bicarbonate: It enters into the circulation and excessive use can result in systemic alkalosis.
Citrate salts: Certain antacids containing citrate salts, such as potassium citrate, can be absorbed systemically and affect the body's acid-base balance.
Non-Systemic Antacids
These antacids function in
the gastrointestinal system with minimal bloodstream absorption. These drugs
relieve acid reflux, indigestion, and heartburn symptoms. Examples include:
Calcium carbonate: It primarily acts locally in the stomach to neutralize acid and does not have significant systemic effects.
Magnesium hydroxide: It works locally to neutralize stomach acid and can also have a laxative effect.
Systemic Antacids
Systemic alkalizers raise blood and body fluid pH. Systemic
hyperacidity and metabolic acidosis are often treated with these drugs. These
drugs may increase bloodstream bicarbonate ions after ingestion. Alkaline
buffers like bicarbonate ions neutralise excess acid and restore acid-base
balance.
Non-systemic Antacids
These have localised effects in the GI tract since they are not
taken into the bloodstream.
1. Acid Neutralization
Antacids contain alkaline
substances that chemically react with stomach acid (hydrochloric acid) to form
salts and water. This neutralization process raises the pH level in the
stomach, reducing the acidity.
2. Mucosal Protection
Some antacids can protect
the stomach lining by forming a barrier. This layer physically protects the
mucosa from acid, reducing irritation and inflammation.
3. Stimulation of Saliva Production
Chewable antacids enhance
saliva production. Bicarbonate ions in saliva temporarily neutralise stomach
acid.
Pharmacological Actions of Antacids
1. Acid Neutralization
Antacids neutralize excess stomach acid. Antacids react with
stomach hydrochloric acid to generate salts and water. Neutralisation raises
stomach pH, decreasing acidity and relieving discomfort. Neutralisation
reaction:
Acid + Antacid →
Salt + Water
Antacids neutralize stomach acid, relieving heartburn and
indigestion. These medications reduce gastric acidity to temporarily relieve
oesophageal reflux.
2. Protection of Gastric Mucosa
Antacids protect the stomach's gastric mucosa. These drugs raise
stomach pH, reducing gastric acid damage. The preventive action may aid gastric
ulcer healing and prevent stomach lining damage.
3. Symptomatic Relief
Antacids relieve acid reflux, GERD, and peptic ulcer symptoms.
Antacids reduce acidity and relieve heartburn, regurgitation, bloating, and
stomach pain.
Pharmacokinetics of Antacids
Absorption
Antacids are typically taken orally and begin to act locally within
the gastrointestinal (GI) tract. They are not significantly absorbed into the
bloodstream and primarily remain within the GI lumen. The absorption of
antacids is minimal, if any, and they do not undergo systemic distribution.
Distribution
Antacids do not undergo significant distribution throughout the
body. They primarily act locally at the site of administration within the GI
tract, where they neutralize excess stomach acid and provide relief from
symptoms.
Metabolism
Antacids are not metabolized in the body. They are generally
considered inert substances that undergo chemical reactions with stomach acid
to neutralize its effects.
Elimination
Antacids are excreted primarily through the gastrointestinal route.
They are eliminated from the body through feces after their action within the
GI tract. Some components of antacids, such as aluminum or magnesium, may be
minimally absorbed and excreted through the kidneys, but the overall systemic
elimination is limited.
Therapeutic Uses of Antacids
1. GERD (Gastroesophageal Reflux Disease)
GERD, which causes chronic
acid reflux and heartburn, is usually treated with antacids. Antacids relieve
symptoms by neutralising stomach acid.
2. Pepticulcers
Peptic ulcers—open sores in
the stomach or upper small intestine—can be treated with antacids. Antacids
neutralise stomach acid and improve ulcer healing.
3. Dyspepsia
Indigestion, or dyspepsia,
causes abdominal pain, bloating, and early satiety. Antacids reduce fullness
and stomach acid to relieve these symptoms.
4. Aspiration Pneumonia
Aspirating stomach contents,
particularly acid, causes pneumonia. Antacids lower stomach acidity and lung
damage.
5. Kidney Stones
Excess urine calcium causes
some kidney stones. Calcium carbonate antacids bond to dietary oxalates,
inhibiting absorption and stone formation.
6. Calcium-Magnesium Supplementation
Antacids with calcium or
magnesium can supply these elements. They may be prescribed to treat
osteoporosis or magnesium insufficiency.
Drug Interactions of Antacids
1. Interference with Absorption
Antacids can reduce the
absorption of certain medications by altering the pH of the stomach or binding
to the medication itself. This can decrease the effectiveness of the affected
medications. Examples include:
2. Antibiotics
Antacids may inhibit the
absorption of tetracyclines, fluoroquinolones, and macrolides. Dividing
antibiotics and antacids by at least two hours improves their efficacy. It's
generally recommended to take antibiotics and antacids at least two hours apart
to minimize this interaction.
3. Iron Supplements
Antacids can decrease the
absorption of iron supplements. If iron supplementation is required, it's
advisable to take iron supplements separately from antacids or consult a
healthcare professional for guidance.
4. Thyroid Medications
Antacids can hinder
levothyroxine absorption. Take these medications many hours apart from
antacids.
5. Drug Inactivation
Antacids can chemically
react with certain medications, resulting in reduced effectiveness. Examples
include:
6. H2Blockers and Proton Pump Inhibitors (PPIs)
Antacids neutralise H2
blockers like ranitidine and PPIs like omeprazole, reducing their
effectiveness. Antacids and acid-blockers should be taken one to two hours
apart.
7. Altered Urinary Excretion
Aluminium and magnesium
antacids can alter kidney excretion of other drugs. This may affect drug levels
in blood.
Quinidine
Antacids inhibit quinidine
excretion, increasing blood levels. Antacids and quinidine should be monitored
closely.
Digoxin
Antacids inhibit digoxin
elimination, increasing blood levels. Antacid therapy requires monitoring and
adjusting digoxin levels.
Adverse Effects of Antacids
1. Constipation
Aluminium or calcium antacids can cause constipation.
2. Diarrhea
Magnesium-containing antacids might cause diarrhoea if used
excessively or for a long time. Magnesium increases intestinal hydration and
gastrointestinal transit, which explains this.
3. Electrolyte Imbalances
Magnesium or sodium bicarbonate antacids can cause electrolyte
imbalances. Increased calcium, potassium, and magnesium excretion may cause
electrolyte imbalances.
4. Acid Rebound
Frequent or long-term antacid use can cause acid rebound. After
continuous antacid use, the body may increase gastric acid production as a
compensatory mechanism, worsening acid-related symptoms.
5. Allergic Reactions
Antacids occasionally cause allergic responses. Symptoms include
skin rash, pruritus, edoema, and respiratory distress. If an allergic response
occurs, seek medical attention immediately.
Contraindication of Antacids
1. Allergic Reactions or Hypersensitivity
Antacids should not be used by people with known allergies or
hypersensitivity.
2. Severe Kidney Disease
Magnesium-containing antacids can cause renal dysfunction and
increase magnesium accumulation.
3. Calcium-Rich Kidney Stones
Calcium-rich kidney stones, such as calcium oxalate or calcium
phosphate stones, may prevent people from utilising calcium-based antacids.
Calcium supplementation can increase stone development in sensitive people.
4. Metabolic Alkalosis
Metabolic alkalosis raises pH. In metabolic alkalosis, avoid bi-carbonate
containing antacids such sodium bicarbonate. These antacids may increase body
alkalinity, worsening the disease.
5. Chronic Use and Underlying Conditions
Antacid use without medical supervision is typically discouraged.
Long-term drug use may mask preexisting diseases like peptic ulcers or GERD,
requiring specific treatment.
Formulations and Doses of Antacids
Antacids are available in various formulations to suit different
preferences and needs. Here are some common formulations of antacids:
1. Tablets/Caplets
Antacids are commonly available in tablet or caplet form. These
solid dosage forms are easy to swallow and often provide a convenient and
portable option for on-the-go relief.
2. Chewable Tablets
Chewable antacids are designed to be chewed thoroughly before
swallowing. They typically have a pleasant taste, making them more palatable
for individuals who prefer not to swallow tablets whole.
3. Effervescent Tablets
Effervescent antacids come in tablet form and are designed to be
dissolved in water before consumption. Once dissolved, they create a fizzy or
effervescent solution that can be consumed to provide relief.
4. Suspensions/Liquids
Antacid suspensions or liquids are available in bottles or sachets.
These formulations are in liquid form and can be directly consumed or mixed
with water for ingestion.
5. Powders
Antacid powders are packaged in single-dose sachets. They can be
mixed with water to form a liquid solution for ingestion.
6. Antacid Gels
Some antacids are formulated as gels, which are thick and viscous
in consistency. These gels can help provide a longer-lasting coating effect on
the stomach lining, offering extended relief.
7. Antacid Chewable Gum
Antacid gum is a unique formulation where the active antacid
ingredients are incorporated into a gum base. Chewing the gum releases the
antacid properties, providing relief from symptoms
Doses of antacids
Calcium
Carbonate
Adult Dose: 500 mg to 2,000
mg
Magnesium
Hydroxide
Adult Dose: 400 mg to 800 mg
as needed
Example: Milk of Magnesia
Aluminum
Hydroxide
Adult Dose: 600 mg to 1200
mg as needed.
Sodium
Bi-carbonate
Adult Dose: 325 mg to 2,000
mg
