Antacids are one of the oldest and most commonly used medications in gastrointestinal (GI) pharmacology. They provide quick relief from symptoms like acidity, heartburn, and indigestion by neutralizing stomach acid. Students often confuse antacids with antihistamines (H2 blockers) or PPIs, but antacids work much faster and act directly in the stomach
This comprehensive guide explains everything about antacids in a clear and student-friendly way — including uses, mechanism, adverse effects, and important nursing responsibilities.
What Are Antacids?
Antacids are alkaline (basic) compounds that react with gastric hydrochloric acid (HCl) to produce water + salt, reducing acidity and elevating stomach pH.
They provide immediate but short-term relief.
Common Antacid Agents
- Aluminum Hydroxide
- Magnesium Hydroxide
- Calcium Carbonate (TUMS)
- Sodium Bicarbonate (less commonly used in modern clinical practice)
Because each compound has different effects, antacids are frequently combined (e.g., Aluminum + Magnesium) to balance side effects.
Classification of Antacids
1. Aluminum Salts
- Example: Aluminum Hydroxide
- Slow acting
- Causes constipation
2. Magnesium Salts
- Example: Magnesium Hydroxide (Milk of Magnesia)
- Fast acting
- Causes diarrhea
3. Calcium Salts
- Example: Calcium Carbonate (TUMS)
- Quick relief
- May cause hypercalcemia, constipation
4. Sodium Bicarbonate
- Systemic antacid
- Risk of alkalosis, fluid retention
- Not preferred in patients with heart or kidney disease.
Mechanism of Action (MOA)
Antacids work by neutralizing gastric acid in the stomach lumen.
How They Act:
- Increase gastric pH
- Reduce activity of pepsin (a stomach enzyme that works only in acidic pH)
- Provide rapid relief from burning sensation and acid reflux
- Do NOT reduce acid production (unlike H2 blockers & PPIs)
- Do NOT treat the underlying cause—only provide symptomatic relief
Example Reaction (Calcium Carbonate):
CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O
This explains why belching or gas may occur after taking calcium carbonate.
Therapeutic Uses of Antacids
Antacids are mainly used for symptomatic relief, not long-term treatment.
Common Indications:
- Acid indigestion
- Heartburn
- Gastroesophageal Reflux Disease (GERD)
- Peptic Ulcer Disease (PUD)
- Stress-induced mucosal irritation
- Dyspepsia (general indigestion)
Not effective for:
- Severe GERD
- Chronic ulcers
- H. pylori infection
- Prevention of GI bleeding
These require H2 blockers or PPIs.
Adverse Effects of Antacids
Side effects vary depending on the compound used.
1. Aluminum Compounds
- Constipation
- Hypophosphatemia (↓P)
- Muscle weakness
- Osteomalacia (with long-term use)
2. Magnesium Compounds
Diarrhea (osmotic effect)- Flushing
- Hypotension
- Reduced deep tendon reflexes
- Arrhythmias (in renal failure patients)
3. Calcium Carbonate
- Constipation
- Hypercalcemia (↑Ca)
- Milk-alkali syndrome (rare)
- Kidney stones (long-term use)
4. Sodium Bicarbonate
- Belching (due to CO₂ release)
- Metabolic alkalosis
- Fluid overload (edema)
- Hypertension worsening
General Adverse Effects (All Antacids)
Electrolyte imbalance (↓P, ↑Ca, ↑Mg)
Abdominal discomfort
- Nausea
- Vomiting
- Bloating
- Diarrhea or constipation
To minimize discomfort, antacids are best taken after meals, when acid secretion is highest.
Drug Interactions
Antacids can reduce absorption or effectiveness of many drugs due to pH changes or binding to the drug.
Important Interactions:
| Drug | Effect of Antacid |
|---|---|
| Ranitidine (H2 blocker) | ↓ absorption |
| Warfarin | ↓ effectiveness |
| Digoxin | ↓ absorption |
| Tetracyclines | Form insoluble complexes → ↓ effectiveness |
| Fluoroquinolones | ↓ absorption |
| Iron supplements | Reduced absorption |
| Levothyroxine | ↓ absorption |
Important rule for students:
Give antacids 1–2 hours before or after other medications.
Contraindications
Antacids should be avoided or used with caution in:
- Renal failure (Mg accumulation risk)
- Hypercalcemia
- Kidney stones
- GI obstruction or perforation
- Heart failure or hypertension (avoid sodium bicarbonate)
- Patients on multiple oral medications
Nursing Considerations
Before Administration:
- Assess GI symptoms
- Check renal function (creatinine, urine output)
- Evaluate electrolyte status
During Administration:
- Give 1–3 hours after meals for best effect
- Encourage patient to chew tablets properly
- Administer magnesium and aluminum combinations to balance stool effects
Patient Education:
- Do not take antacids with milk (risk of milk-alkali syndrome)
- Avoid taking antacids with other medicines
- Do not overuse antacids—can lead to chronic electrolyte disturbances
- Report symptoms like black stools, persistent pain, or vomiting
Comparison: Antacids vs. H2 Blockers vs. PPIs
| Feature | Antacids | H2 Blockers | Proton Pump Inhibitors (PPIs) |
|---|---|---|---|
| Onset of Action | Very fast | 30–60 minutes | Slow (1–2 days for full effect) |
| Duration | Short (2–3 hours) | Intermediate | Long-lasting |
| Mechanism | Neutralizes acid | Blocks H2 receptors | Blocks acid pump (H⁺/K⁺ ATPase) |
| Use | Symptomatic relief | Mild–moderate GERD | GERD, ulcers, severe acidity |
| OTC Availability | Yes | Yes | Yes (low dose) |
Frequently Asked Questions (FAQs)
1. Do antacids cure acidity permanently?
No. Antacids only neutralize acid temporarily. They do not reduce acid production or treat underlying diseases.
2. Can antacids be taken with milk?
No. Milk + calcium carbonate may cause milk-alkali syndrome. Avoid this combination.
3. How long do antacids take to work?
Antacids start working within 5–10 minutes, making them the fastest-acting acid-relief medicine.
4. Can pregnant women take antacids?
Calcium and magnesium-based antacids are generally safe, but always consult a doctor. Avoid sodium bicarbonate.
5. Why do magnesium antacids cause diarrhea?
Magnesium salts pull water into the intestine → osmotic diarrhea.
6. When should antacids be avoided?
Avoid in kidney failure, hypercalcemia, severe hypertension, or when taking drugs like tetracyclines or digoxin.
7. Are antacids addictive?
Not in the medical sense, but people may overuse them for quick relief. Long-term overuse can cause serious complications.
