Antacids

Definition and Therapeutic Purpose

Antacids are over-the-counter or prescription medications that neutralize gastric acid in the stomach lumen to provide rapid symptomatic relief of heartburn, indigestion, epigastric discomfort, and acid reflux

They do not prevent acid secretion but act by directly neutralizing hydrochloric acid already present in the gastric content

They are typically used for short-term symptom management of conditions such as gastroesophageal reflux disease (GERD), peptic ulcer disease (PUD), functional dyspepsia, and acid-related gastritis

Mechanism of Action

Antacids work via a simple acid-base neutralization reaction between weak bases (metal salts) and hydrochloric acid in the stomach

This reaction raises gastric pH, reduces proteolytic activity of pepsin, and provides mucosal protection

Some formulations also adsorb bile acids and stimulate prostaglandin secretion which further enhances mucosal defense

Most act within minutes but have a short duration of action (30 minutes to 2 hours), hence multiple doses may be needed daily

Common Active Ingredients and Their Profiles

Aluminum hydroxide

Slower acting but longer duration

Constipating effect

Binds phosphate in the gut and may cause hypophosphatemia in chronic use

Magnesium hydroxide

Rapid onset of action

Laxative effect may cause diarrhea

Often combined with aluminum hydroxide to balance bowel side effects

Calcium carbonate

Fast-acting, potent neutralization

May cause acid rebound (stimulation of acid after initial buffering)

Risk of hypercalcemia and milk-alkali syndrome with excessive use

Sodium bicarbonate

Very rapid action

Short duration

Systemically absorbed – may cause metabolic alkalosis, hypernatremia, fluid retention

Used cautiously in hypertension, CHF, and renal impairment

Magaldrate

A complex of aluminum and magnesium hydroxide

Provides balanced acid neutralization

Minimal GI side effects

Hydrotalcite

A layered double hydroxide combining aluminum and magnesium

Slower onset but sustained release

Simethicone (added in many formulations)

Anti-foaming agent that reduces gas bubbles in the stomach and intestines

Has no acid-neutralizing capacity

Examples of Antacid Products and Brand Combinations

Aluminum hydroxide + Magnesium hydroxide – Maalox, Mylanta

Calcium carbonate – Tums, Rolaids

Magnesium hydroxide + Aluminum hydroxide + Simethicone – Gelusil

Sodium bicarbonate – Alka-Seltzer

Hydrotalcite – Talcid

Magaldrate – Riopan

Therapeutic Uses

Dyspepsia

Relieves epigastric burning, bloating, early satiety

Gastroesophageal reflux disease (GERD)

Used for rapid symptom control in mild or intermittent GERD

Not effective for healing erosive esophagitis

Peptic ulcer disease (PUD)

Provides short-term relief of ulcer-related pain

Does not eradicate H. pylori or promote mucosal healing alone

Functional heartburn or non-cardiac chest pain

Can help distinguish GERD from other causes by symptom response

Drug-induced gastritis (e.g., NSAID-related)

Adjunct to PPIs for symptomatic control

Adjunctive Therapy in Dialysis

Aluminum hydroxide occasionally used to bind phosphate in hyperphosphatemia (limited due to toxicity)

Contraindications

Absolute

Known hypersensitivity to components

Calcium-based antacids in patients with hypercalcemia

Sodium bicarbonate in patients with metabolic alkalosis

Relative

Severe renal impairment due to risk of aluminum or magnesium accumulation

Heart failure or hypertension (for sodium-containing preparations)

Chronic constipation (with aluminum) or diarrhea (with magnesium)

Precautions

Avoid long-term or excessive use due to risk of electrolyte imbalance

Monitor serum calcium, phosphate, and magnesium in chronic users

Avoid concurrent use with enteric-coated tablets (altered absorption)

Adverse Effects

Calcium carbonate

Constipation

Hypercalcemia

Milk-alkali syndrome with excessive use

Aluminum hydroxide

Constipation

Hypophosphatemia with prolonged use

Neurotoxicity in renal insufficiency

Magnesium hydroxide

Diarrhea

Hypermagnesemia in renal failure (bradycardia, hypotension, CNS depression)

Sodium bicarbonate

Metabolic alkalosis

Bloating due to CO₂ release

Exacerbates fluid retention and hypertension

Drug Interactions

Chelation or pH-mediated reduced absorption

Tetracyclines: form insoluble complexes

Quinolones: reduced bioavailability

Iron supplements: decreased absorption

Levothyroxine: impaired absorption

Azole antifungals (e.g. ketoconazole): reduced efficacy due to pH rise

Digoxin: reduced absorption

To avoid these interactions, antacids should be administered at least 2 hours before or 4 hours after affected drugs

Special Populations

Pregnancy

Generally considered safe if used occasionally and within recommended doses

Calcium and magnesium-based antacids preferred

Avoid sodium bicarbonate due to fluid overload risk

Pediatrics

Avoid prolonged use

Dose should be age- and weight-appropriate

Avoid aluminum-containing formulations in neonates

Elderly

More susceptible to electrolyte imbalances and drug interactions

Cautious use in those with chronic kidney disease

Renal Impairment

Avoid aluminum and magnesium salts due to risk of accumulation

Calcium carbonate may be safer but still monitor electrolytes

Advantages

Rapid symptom relief

Available over-the-counter

Minimal systemic absorption in most agents

Relatively inexpensive

Can be used on-demand

Limitations

Short duration of action

Do not treat underlying cause

Not effective in moderate to severe GERD or erosive disease

Frequent dosing required for sustained effect

May interfere with nutrient and drug absorption

Not curative in peptic ulcer disease

Clinical Considerations

Used mainly for acute symptom relief or as adjuncts to H2 blockers and PPIs

Onset of action within minutes, but duration is short so repeated dosing may be required

Space antacids away from other oral medications due to absorption interference

Excessive or prolonged use may result in rebound acidity or electrolyte disturbances

Patients with GERD or ulcers should be assessed for long-term acid suppression strategies

Comparison with Other Acid-Related Therapies

Antacids act by neutralizing existing acid, whereas H2 receptor antagonists (e.g. ranitidine, famotidine) and proton pump inhibitors (e.g. omeprazole, esomeprazole) reduce acid production at the source

Antacids are faster acting but provide shorter symptom control

PPIs and H2 blockers are more effective for healing mucosal damage and preventing recurrence

Counseling Points for Patients

Chew chewable tablets thoroughly before swallowing

Liquid forms may provide more rapid relief

Do not exceed recommended daily dose

Avoid taking with other oral medications unless advised otherwise

Report persistent or worsening symptoms, which may suggest serious GI conditions

Do not substitute antacids for prescribed ulcer or GERD therapy unless directed

Antacid Misuse and Overuse

Chronic, unsupervised use may mask serious conditions such as gastric ulcers or malignancy

Alkalosis and electrolyte derangements may occur with misuse

Excessive calcium-based antacids may result in nephrocalcinosis or renal stones

Routine antacid use should prompt evaluation for GERD, peptic ulcer disease, or H. pylori infection

Therapeutic Summary

Antacids are among the oldest and most frequently used medications for gastrointestinal symptom relief

They provide immediate, short-term control of hyperacidity and are widely accessible

Appropriate selection based on individual tolerance, comorbidities, and drug interactions ensures safe and effective use

Antacids remain valuable as adjunctive therapy in many acid-related disorders when used with care and clinical supervision