What is the recommended dose of Pepcid (Famotidine) for treating allergies?

Pepcid (Famotidine) Dosing for Allergic Reactions

For acute allergic reactions and anaphylaxis, famotidine is dosed at 1-2 mg/kg (maximum 75-150 mg) intravenously or orally in the hospital setting, and is NOT recommended as monotherapy but only as adjunctive treatment to epinephrine. 1

Context and Role in Allergy Treatment

Famotidine (Pepcid) is an H2-antihistamine that serves as second-line adjunctive therapy only in allergic reactions—it should never be used alone or as a substitute for epinephrine in anaphylaxis. 1 The combination of H1-antihistamines (like diphenhydramine) with H2-antihistamines (like famotidine or ranitidine) is superior to H1-antihistamines alone, but both have a much slower onset of action than epinephrine. 1

Specific Dosing Recommendations

In Hospital-Based Settings (Acute Anaphylaxis)

For children:

• 1-2 mg/kg per dose 1
• Maximum dose: 75-150 mg (oral or IV) 1

For adults:

• Maximum dose: 75-150 mg (oral or IV) 1

The guidelines specifically mention ranitidine dosing (another H2-blocker) as 50 mg in adults and 12.5-50 mg (1 mg/kg) in children, which can be diluted and given IV over 5 minutes. 1 While famotidine is not explicitly dosed in the older anaphylaxis guidelines, the NIAID food allergy guidelines provide the weight-based dosing above. 1

At Discharge (Post-Anaphylaxis)

H2-antihistamine (ranitidine or famotidine):

• Twice daily for 2-3 days 1
• This is given alongside H1-antihistamines and corticosteroids as part of post-discharge adjunctive therapy 1

Critical Clinical Caveats

Never use famotidine as first-line treatment. Epinephrine is the only first-line treatment for anaphylaxis—intramuscular epinephrine 0.01 mg/kg (maximum 0.5 mg) must be given immediately. 1 Famotidine and other H2-blockers are added only after epinephrine administration.

Onset of action is slow. H2-antihistamines take significantly longer to work than epinephrine, which is why they cannot be relied upon for acute life-threatening reactions. 1

Prophylactic use in allergic patients: Research suggests that combined H1 and H2-receptor antagonist premedication (chlorpheniramine plus famotidine) can prevent histamine release in allergic patients undergoing procedures, though this is not standard practice for routine allergic reactions. 2

Practical Algorithm for Use

1. Acute anaphylaxis: Give IM epinephrine first (0.01 mg/kg, max 0.5 mg) 1
2. Add famotidine as adjunctive therapy: 1-2 mg/kg IV/oral (max 75-150 mg) 1
3. Continue at discharge: Famotidine twice daily for 2-3 days 1
4. Monitor: Famotidine is well-tolerated with minimal drug interactions and primarily renal elimination 3

Important note: While famotidine itself can rarely cause anaphylactic reactions, this is exceedingly uncommon. 4 Cross-reactivity between different H2-blockers has not been demonstrated, so alternative H2-blockers can be used if famotidine causes a reaction. 4