What are the doses of Solumedrol (methylprednisolone) and Pepcid (famotidine) for treating an allergic reaction?

Methylprednisolone and Famotidine Dosing for Allergic Reactions

For allergic reactions, administer methylprednisolone 1-2 mg/kg IV every 6 hours (maximum 60-80 mg per dose) and famotidine 20 mg IV, but remember that epinephrine is the only first-line treatment for anaphylaxis—these medications are strictly adjunctive. 1, 2, 3

Critical First: Epinephrine Must Come First

Before discussing steroid and H2-blocker dosing, you must understand that corticosteroids and antihistamines are never first-line therapy for anaphylaxis—they provide no acute benefit and their anti-inflammatory effects take 6-12 hours to manifest. 2, 3

• Epinephrine 0.01 mg/kg IM (maximum 0.5 mg) into the anterolateral thigh is the only first-line treatment, repeated every 5-15 minutes as needed 1, 3
• Never delay epinephrine to give steroids or antihistamines 2, 3

Methylprednisolone (Solu-Medrol) Dosing

Standard Dosing for Hospital-Based Management

• 1-2 mg/kg IV every 6 hours (this is the weight-based dose) 1, 2, 3
• For a 70 kg adult: 70-140 mg per dose every 6 hours, though 40 mg IV every 6 hours is commonly used in practice 3
• Maximum single dose: 60-80 mg 1, 2

Pediatric Dosing

• Same weight-based dosing applies: 1-2 mg/kg IV every 6 hours 2, 3
• Continue until stabilization, typically 48-72 hours 2

Alternative Corticosteroid Options

• Prednisone 1 mg/kg orally (maximum 60-80 mg) for less severe reactions or at discharge 1
• Hydrocortisone 100 mg IV is an acceptable alternative 3

Famotidine (Pepcid) Dosing

Adult Dosing

• 20 mg IV every 12 hours (this is the FDA-approved dose for hospitalized patients) 4
• Can also use 50 mg IV as a single dose for acute allergic reactions 3
• The combination of H1 + H2 antihistamines is superior to H1 alone 3

Pediatric Dosing

• 0.25 mg/kg IV every 12 hours (maximum 40 mg/day) 4
• Administer over at least 2 minutes or as a 15-minute infusion 4

Preparation and Administration

• Dilute 2 mL of famotidine injection (10 mg/mL) with 0.9% sodium chloride to 5-10 mL total volume 4
• Inject over at least 2 minutes, or dilute in 100 mL and infuse over 15-30 minutes 4

Complete Treatment Algorithm for Allergic Reactions

Immediate Actions (0-5 minutes)

• Epinephrine 0.01 mg/kg IM (0.3-0.5 mg for adults, 0.15 mg for children 10-25 kg) into anterolateral thigh 1, 3
• Position patient supine with legs elevated (unless respiratory distress) 3
• Establish IV access and give 500-1000 mL crystalloid bolus (20 mL/kg for children) 3

Within 5-15 Minutes (Adjunctive Therapy)

• Methylprednisolone 1-2 mg/kg IV every 6 hours 1, 2, 3
• Diphenhydramine 25-50 mg IV (1-2 mg/kg, maximum 50 mg) 1, 3
• Famotidine 20 mg IV (or ranitidine 50 mg IV if available) 1, 3
• Albuterol nebulization if bronchospasm persists (2.5-5 mg in 3 mL saline) 1, 3

Ongoing Management

• Repeat epinephrine every 5-15 minutes if symptoms persist 1, 3
• Continue methylprednisolone every 6 hours for 48-72 hours 2
• Observe for at least 6 hours (longer for severe reactions) 3

Special Considerations and Pitfalls

Patients on Beta-Blockers

• May be refractory to epinephrine 3
• Glucagon 1-5 mg IV over 5 minutes (20-30 mcg/kg for children, maximum 1 mg), followed by infusion of 5-15 mcg/min 1, 3

Renal Insufficiency

• For creatinine clearance <50 mL/min: reduce famotidine dose to 10 mg IV every 12 hours or extend interval to 36-48 hours 4
• Methylprednisolone dosing does not require adjustment 2

Critical Pitfall: Corticosteroid Allergy

• Paradoxically, patients can have allergic reactions to methylprednisolone itself, particularly asthmatics and those receiving high doses 5, 6, 7
• If worsening symptoms occur after steroid administration, consider this possibility 5
• Administer high doses (≥500 mg) over 30-60 minutes and observe closely 5

Discharge Medications

• Continue oral prednisone 0.5-1 mg/kg daily for 2-3 days 1
• H1 antihistamine (diphenhydramine) every 6 hours for 2-3 days 1
• H2 antihistamine (famotidine 20 mg twice daily or ranitidine) for 2-3 days 1
• Prescribe two epinephrine auto-injectors with training 1, 3

Evidence Quality Note

The steroid dosing recommendations come from NIAID expert panel guidelines (2010) 1 and are reinforced by recent high-quality guideline summaries 2, 3. However, the evidence supporting corticosteroids for preventing biphasic reactions is only moderate, and they provide no benefit in the acute phase 1, 2. The famotidine dosing is directly from FDA labeling 4, making it the most authoritative source for this specific medication.