What medications are alkaline when they enter the stomach?

Alkaline Medications in the Stomach

Antacids are the primary medications that are alkaline when they enter the stomach, specifically calcium carbonate, aluminum hydroxide, magnesium hydroxide, and sodium bicarbonate. These medications are designed to neutralize gastric acid by raising the pH of the stomach contents 1.

Types of Alkaline Medications

Antacids

Antacids work by directly buffering gastric acid in the esophagus or stomach to reduce heartburn and promote mucosal healing. They consist of various compounds that have alkaline properties:

1. Calcium Carbonate (CaCO₃)

   • Common brand: Tums
   • Rapidly neutralizes stomach acid
   • Can cause "acid rebound" - a paradoxical increase in acid secretion after the neutralizing effect wears off 2, 3
   • Has excellent acid-neutralizing capacity 3

2. Aluminum/Magnesium Hydroxide Combinations

   • Common brand: Mylanta
   • Provides longer duration of action in the esophagus (82 minutes) compared to calcium carbonate (60 minutes) 2
   • More effective at increasing both esophageal and gastric pH than calcium carbonate 2
   • Magnesium hydroxide alone can cause diarrhea; aluminum hydroxide can cause constipation

3. Sodium Bicarbonate

   • Rapidly neutralizes acid
   • Highly systemic (absorbed into bloodstream)
   • Can cause metabolic alkalosis and alkaliuria 4
   • Contains high sodium content which may lead to fluid retention 4

Proton Pump Inhibitors (PPIs)

While not alkaline themselves, PPIs like omeprazole reduce acid production, which can result in a less acidic stomach environment:

• Omeprazole and other PPIs are acid-labile and are formulated as enteric-coated granules to prevent degradation in the stomach 5
• They begin to work only after leaving the stomach and being absorbed in the small intestine 5

H2-Receptor Antagonists

H2-blockers like ranitidine are not alkaline but reduce acid production:

• They begin to increase gastric pH within 30 minutes of administration 6
• Effects last approximately 6 hours 6

Clinical Implications of Alkaline Medications

Drug Interactions

1. Antacids can affect other medications by:

   • Changing gastric pH, altering drug dissolution 1
   • Adsorption or chelation of other drugs 1
   • Altering drug elimination by changing urinary pH 1

2. Specific timing considerations:

   • P-aminosalicylic acid should be administered 1 hour before or 2 hours after meals; should not be administered with aluminum and magnesium-containing antacids 6

Adverse Effects

1. Calcium-containing antacids:

   • Can cause acid rebound phenomenon 2, 3
   • May contribute to renal stone formation due to urinary pH elevation 4

2. Aluminum-containing antacids:

   • Can cause phosphorus depletion with long-term use 4
   • May lead to aluminum deposition in brain tissue in patients with renal insufficiency 4

3. Magnesium-containing antacids:

   • Can lead to hypermagnesemia in patients with renal impairment 4

4. Sodium bicarbonate:

   • Can cause metabolic alkalosis 4
   • High sodium content may lead to fluid retention 4

Formulation Effects on Alkalinity

The physical formulation of antacids can affect their alkaline properties and effectiveness:

• Liquid suspensions (like Talcid suspension) may have better barrier properties similar to gastric mucus 7
• Tablet formulations (when powdered) may reduce the barrier function of gastric mucus 7

Practical Considerations

When managing patients with acid-related disorders:

• For short-term symptom relief, antacids provide rapid but brief acid neutralization
• For patients requiring concomitant medications, be aware of potential interactions with antacids
• In patients with renal insufficiency, avoid aluminum and magnesium-containing antacids due to risk of toxicity 4
• For patients with sodium restriction, avoid sodium bicarbonate antacids 4

While antacids were once first-line therapy for acid-related disorders, they have largely been replaced by PPIs and H2-receptor antagonists for conditions like GERD and peptic ulcer disease 1. However, they remain useful for short-term symptom relief and specific indications like non-ulcer dyspepsia.