What is the recommended dosage and usage of H2 (histamine-2) blockers, such as ranitidine (Zantac) or famotidine (Pepcid), for patients requiring acid reduction?

H2 Blocker Dosing and Usage

For acid reduction therapy, famotidine 20-40 mg daily or ranitidine 150 mg twice daily are the standard recommended doses, with famotidine being the preferred agent due to its superior potency (20-50 times more potent than cimetidine), longer duration of action, and lack of drug interactions with the cytochrome P-450 system. 1, 2

Standard Dosing Regimens

Famotidine (Preferred Agent)

• Duodenal ulcer: 40 mg once daily at bedtime OR 20 mg twice daily 3
• Gastric ulcer: 40 mg once daily at bedtime 3
• GERD (symptomatic): 20 mg twice daily (superior to 40 mg at bedtime) 3
• Erosive esophagitis: 40 mg twice daily 3
• Maintenance therapy: 20 mg at bedtime 3
• Pathological hypersecretory conditions: 20-160 mg every 6 hours, titrated to maintain basal acid secretion <10 mEq/hour 3

Ranitidine (Alternative Agent)

• Duodenal ulcer: 150 mg twice daily OR 300 mg once daily at bedtime 4
• Gastric ulcer: 150 mg twice daily 4
• GERD: 150 mg twice daily 4
• Erosive esophagitis: 150 mg four times daily 4
• Maintenance therapy: 150 mg at bedtime 4
• Pathological hypersecretory conditions: 150 mg twice daily, may increase frequency as needed up to 6 g/day 4

Pediatric Dosing

For children 1 month to 16 years, ranitidine 5-10 mg/kg/day divided in 2-3 doses is FDA-approved, with both agents demonstrating very rare side effects in pediatric populations. 1, 4

• Treatment of active ulcers: 2-4 mg/kg twice daily (maximum 300 mg/day) 4
• Maintenance therapy: 2-4 mg/kg once daily (maximum 150 mg/day) 4
• GERD/erosive esophagitis: 5-10 mg/kg/day in 2 divided doses 4

Clinical Selection Algorithm

Choose Famotidine When:

• Patient is on dual antiplatelet therapy (especially clopidogrel): Famotidine does not interfere with clopidogrel's antiplatelet activity, unlike PPIs 1, 5
• Concern for drug interactions exists: Famotidine does not interact with cytochrome P-450 system 1, 2
• Maximum potency is needed: Famotidine is 8-9 times more potent than ranitidine with longer duration of action 1, 2

Choose Ranitidine When:

• Cost is a primary concern: Both agents are equally effective at standard doses 1
• Pediatric FDA-approved indication is required: Ranitidine has specific pediatric labeling 4

Switch to PPIs When:

• Long-term therapy (>6 weeks) is needed: Both H2 blockers develop tachyphylaxis within 6 weeks, limiting long-term effectiveness 1, 6
• Erosive esophagitis requires healing: PPIs provide superior healing rates and symptom relief compared to H2 blockers 7, 8
• Patient is H. pylori-positive with NSAID use: PPIs are more effective in this scenario 1

Critical Limitations and Pitfalls

Tachyphylaxis develops within 6 weeks of continuous H2 blocker therapy, significantly reducing their effectiveness for long-term acid suppression. 1, 6

• H2 blockers at standard doses prevent NSAID-related duodenal ulcers but NOT gastric ulcers; double doses are required for gastric ulcer protection 1
• For Barrett's esophagus, PPIs are superior to H2 blockers for both symptom control and dysplasia prevention (OR 0.25 for PPIs vs H2 blockers) 7
• In erosive esophagitis, H2 blockers achieve only 40-50% endoscopic healing rates compared to superior PPI efficacy 8

Special Populations

Renal Impairment

For creatinine clearance <50 mL/min, reduce ranitidine to 150 mg every 24 hours; may increase to every 12 hours if needed with caution. 4

• Time dosing to coincide with end of hemodialysis when applicable 4
• Elderly patients require dose adjustment due to decreased renal function 4

Acute Anaphylaxis Management

In infusion reactions, combine H1 and H2 antagonists: diphenhydramine 25-50 mg IV plus ranitidine 50 mg IV (diluted in 5% dextrose to 20 mL total volume) over 5 minutes. 7

• Combined H1/H2 blockade is superior to either agent alone 7