Is Pepcid (famotidine) used to treat allergic reactions?

Famotidine (Pepcid) for Allergic Reactions

Famotidine (Pepcid) should not be used as a first-line treatment for allergic reactions, but may be used as an adjunctive therapy alongside H1 antihistamines after epinephrine administration in cases of anaphylaxis. 1, 2

Role of H2 Antihistamines in Allergic Reactions

• H2 antihistamines like famotidine are considered adjunctive therapy for allergic reactions and should not be substituted for first-line treatments 1
• Minimal evidence supports the use of H2 antihistamines alone in the emergency treatment of anaphylaxis 1
• H2 antihistamines are typically used concurrently with H1 antihistamines (like diphenhydramine) for relief of symptoms, though rigorous studies supporting this approach in anaphylaxis are lacking 1
• The combination of H1 and H2 antihistamines works better than either one alone for treating certain symptoms of allergic reactions, particularly urticaria 2, 3

Proper Treatment Algorithm for Allergic Reactions

First-line Treatment

• Epinephrine is the only first-line treatment for anaphylaxis with no substitute 1
• Epinephrine should be administered immediately for severe allergic reactions (diffuse hives, shortness of breath, respiratory symptoms, obstructive swelling, or circulatory symptoms) 1

Second-line/Adjunctive Treatments

• H1 antihistamines (e.g., diphenhydramine) for relieving itching and urticaria 1
• H2 antihistamines (e.g., famotidine, ranitidine) may be used concurrently with H1 antihistamines 1, 2
• For mild allergic symptoms (e.g., a few hives, mild nausea/discomfort), antihistamines alone may be appropriate 1

Specific Uses of Famotidine in Allergic Reactions

• Famotidine is typically administered as part of adjunctive treatment for allergic reactions, not as a standalone treatment 2
• For ongoing management after discharge following anaphylaxis, H2 antihistamines like ranitidine are recommended twice daily for 2-3 days 1, 2
• Famotidine should never be used as a substitute for epinephrine in anaphylaxis 1

Important Cautions

• Famotidine itself can rarely cause allergic reactions, including anaphylaxis 4, 5
• There may be cross-reactivity between different H2-receptor antagonists (famotidine, nizatidine, ranitidine) in patients who have experienced allergic reactions to one of these medications 5
• Using antihistamines (including H2 blockers) as the primary treatment is the most common reason reported for not using epinephrine and may place patients at significantly increased risk for progression toward life-threatening reactions 1

Evidence for Combination Therapy

• For treatment of urticaria, the combination of H1 and H2 antihistamines (diphenhydramine plus cimetidine) has been shown to be more effective than H1 antihistamines alone 3
• H2 antihistamines like famotidine may provide additional benefit when combined with H1 antihistamines in treating certain symptoms of allergic reactions 6

Best Practice Recommendations

• For mild allergic reactions: H1 antihistamines are the mainstay of treatment 1, 7
• For severe allergic reactions/anaphylaxis: Epinephrine first, followed by H1 antihistamines, H2 antihistamines, and corticosteroids as adjunctive therapy 1, 2
• Never delay epinephrine administration to give antihistamines in cases of anaphylaxis 1