What dose of oral Benadryl (diphenhydramine) and famotidine should I use if I'm having an allergic reaction?

Dosing of Oral Benadryl and Famotidine for Allergic Reactions

For an allergic reaction, take 25-50 mg of oral diphenhydramine (Benadryl) and 20-40 mg of famotidine. 1

Detailed Medication Protocol

First-Line Treatment

• Epinephrine is the first-line treatment for anaphylaxis (severe allergic reaction)
  • If you have signs of anaphylaxis (difficulty breathing, throat swelling, dizziness, or severe symptoms affecting multiple body systems), use epinephrine immediately and call emergency services
  • Do not rely on antihistamines alone for anaphylaxis

Antihistamine Dosing for Mild to Moderate Allergic Reactions

1. Diphenhydramine (Benadryl)

   • Adult dose: 25-50 mg orally 1
   • Take every 6 hours as needed for 2-3 days 1
   • Maximum daily dose: 300 mg (but typically not more than 200 mg is recommended)

2. Famotidine (H2 blocker)

   • Adult dose: 20-40 mg orally 1
   • Take twice daily for 2-3 days 1

Treatment Algorithm Based on Reaction Severity

For Mild Reactions (localized hives, mild itching, mild rash)

• Diphenhydramine 25 mg orally
• Famotidine 20 mg orally
• Monitor for progression of symptoms

For Moderate Reactions (widespread hives, significant itching, facial swelling without airway compromise)

• Diphenhydramine 50 mg orally
• Famotidine 40 mg orally
• Monitor closely for signs of progression

For Severe Reactions/Anaphylaxis (difficulty breathing, throat swelling, dizziness, vomiting)

• Use epinephrine auto-injector if available
• Call emergency services (911)
• Position lying flat with legs elevated if possible
• After epinephrine, can take diphenhydramine 50 mg and famotidine 40 mg if able to swallow safely

Important Considerations

• Liquid diphenhydramine is more rapidly absorbed than tablets 1
• The combination of H1 antihistamine (diphenhydramine) and H2 antihistamine (famotidine) is superior to diphenhydramine alone 1
• Diphenhydramine causes sedation and may impair driving or operating machinery 2
• Consider non-sedating antihistamines (like fexofenadine) for daytime use if sedation is a concern 1, 2

Common Pitfalls to Avoid

• Do not delay epinephrine if signs of anaphylaxis are present; antihistamines are secondary treatments
• Do not rely solely on antihistamines for severe allergic reactions 1
• Be aware that diphenhydramine can rarely cause acute dystonic reactions (muscle spasms, facial distortion) 3
• Exceeding recommended doses of diphenhydramine increases risk of side effects including confusion, urinary retention, and anticholinergic effects

If symptoms don't improve within 30-60 minutes of taking these medications or if symptoms worsen at any point, seek immediate medical attention.