31.1 Antacids

Antacids for Treating Hyperacidity and Gastrointestinal Disorders

Antacids are among the most commonly used over-the-counter medications for acid-related GI complaints. They work by directly neutralizing stomach acid, which makes them fast-acting but temporary in their relief. For nurses, understanding the differences between antacid formulations matters because each type carries distinct side effects, drug interactions, and patient considerations.

Mechanism of Action and Common Ingredients

Antacids are weak bases that neutralize hydrochloric acid ($HCl$) already present in the stomach, raising gastric pH. This provides symptomatic relief from hyperacidity, heartburn, dyspepsia, and peptic ulcer discomfort. They do not reduce acid production; they only buffer what's already there.

The four main antacid ingredients you need to know:

• Calcium carbonate ($CaCO_3$): Found in Tums, Rolaids. The most potent neutralizer per dose.
• Magnesium hydroxide ($Mg(OH)_2$): Found in Milk of Magnesia. Often combined with aluminum-based antacids.
• Aluminum hydroxide ($Al(OH)_3$): Found in Gaviscon, Mylanta formulations. Slower acting but longer lasting.
• Sodium bicarbonate ($NaHCO_3$): Found in Alka-Seltzer, baking soda. Very fast onset but high sodium load.

Advantages and Disadvantages of Different Formulations

Each antacid type has a distinct profile of benefits and risks. A helpful memory trick: calcium and aluminum constipate, magnesium causes diarrhea.

Calcium carbonate

• Rapid onset, high acid-neutralizing capacity, and doubles as a calcium supplement
• Drawbacks: can cause constipation, acid rebound (the stomach compensates by producing more acid), and hypercalcemia with excessive use

Magnesium hydroxide

• Rapid onset with a laxative effect, which can actually benefit patients who are constipated
• Drawbacks: can cause diarrhea and hypermagnesemia, especially dangerous in patients with renal impairment

Aluminum hydroxide

• Prolonged duration of action with minimal systemic absorption
• Drawbacks: slow onset, causes constipation, and long-term use can lead to phosphate depletion (aluminum binds dietary phosphate in the gut)

Combination products (e.g., Maalox, Mylanta) pair magnesium with aluminum to balance the constipating and diarrheal effects against each other. These are commonly preferred for this reason, though drug interaction risks still apply.

Sodium bicarbonate

• Fastest onset of all antacids
• Drawbacks: high sodium content makes it inappropriate for patients with heart failure, hypertension, or sodium-restricted diets. Systemic absorption can cause metabolic alkalosis with repeated dosing.

Drug Interactions and Adverse Effects

Antacids interfere with other medications in two main ways: they raise gastric pH (which changes how some drugs dissolve and absorb), and some ingredients physically bind to other drugs in the gut.

Key drugs affected include:

• Tetracyclines and fluoroquinolones (antibiotics): antacids chelate these, dramatically reducing absorption
• Iron supplements: absorption significantly decreased
• Levothyroxine: reduced absorption can lead to subtherapeutic thyroid levels

Adverse effects by type:

Patients with renal impairment deserve extra caution. They cannot efficiently clear magnesium or aluminum, putting them at higher risk for toxicity with these formulations.

Patient Education for Antacid Administration

Proper timing and dosing make a real difference in both effectiveness and safety.

Timing:

1. Take antacids 1 hour after meals and at bedtime for best symptom control. Taking them with food shortens their duration because the stomach empties faster.
2. Space antacids at least 2 hours before or after other medications.

Dosing:

• Follow the product label or provider's instructions closely.
• Do not exceed the recommended daily dose. Patients sometimes assume OTC means unlimited, so reinforce this point.

Additional teaching points:

• Encourage lifestyle modifications: avoiding trigger foods (spicy, fatty, acidic), eating smaller meals, not lying down right after eating, and elevating the head of the bed for nighttime symptoms.
• Advise patients to contact their provider if symptoms persist beyond 2 weeks or worsen despite regular antacid use, as this may indicate GERD, peptic ulcer disease, or another condition requiring different treatment.
• Teach patients to recognize and report side effects, particularly persistent diarrhea, constipation, or signs of electrolyte imbalance (muscle weakness, confusion, irregular heartbeat).