Which ICD-10 code should I use for prescribing Pepcid (famotidine) for an allergic reaction?

ICD-10 Coding for Pepcid (Famotidine) in Allergic Reactions

When prescribing Pepcid (famotidine) as adjunctive therapy for allergic reactions, use ICD-10 code T78.40XA (Allergy, unspecified, initial encounter) or the more specific code for the type of allergic reaction being treated, such as T78.3XXA for angioedema or L50.0 for allergic urticaria.

Understanding the Clinical Context

Famotidine is an H2 antihistamine that serves as adjunctive therapy only in allergic reactions, never as first-line treatment. 1 The American Academy of Allergy, Asthma, and Immunology emphasizes that H2 antihistamines like famotidine should be used in combination with H1 antihistamines, as this combination works better than either agent alone. 1

Primary ICD-10 Coding Options

For General Allergic Reactions

• T78.40XA - Allergy, unspecified, initial encounter (most commonly used for general allergic reactions) 2
• T78.3XXA - Angioedema, initial encounter (if swelling is the primary manifestation)
• L50.0 - Allergic urticaria (if hives are the primary presentation)

For Anaphylaxis

• T78.2XXA - Anaphylactic shock, unspecified, initial encounter 2
• T88.6XXA - Anaphylactic reaction due to adverse effect of correct drug or medicament properly administered 3

For Food-Related Allergic Reactions

• T78.00XA - Anaphylactic reaction due to unspecified food, initial encounter
• T78.1XXA - Other adverse food reactions, not elsewhere classified 2

Important Clinical Considerations

Proper Treatment Algorithm

The American Academy of Allergy, Asthma, and Immunology is clear that epinephrine is the only first-line treatment for anaphylaxis, and using antihistamines (including H2 blockers like famotidine) as primary treatment is the most common reason for not using epinephrine, which may place patients at significantly increased risk for life-threatening reactions. 1

Dosing When Famotidine is Appropriate

When used as adjunctive therapy after epinephrine administration, famotidine should be dosed at 1-2 mg/kg per dose with a maximum of 75-150 mg oral or IV. 1 For post-discharge management, continue famotidine twice daily for 2-3 days. 4, 1

Critical Pitfall to Avoid

Never delay epinephrine administration to give antihistamines in cases of anaphylaxis. 1 Famotidine has minimal evidence supporting its use alone in emergency treatment of anaphylaxis. 1

Coding for Specific Scenarios

Mild Allergic Reactions (Appropriate for H2 Antihistamine Use)

For milder reactions such as flushing, urticaria, or isolated mild angioedema where H1 and H2 antihistamines are appropriate:

• Use L50.0 for allergic urticaria
• Use T78.3XXA for angioedema
• Use T78.40XA for unspecified allergic reaction 4

Severe Reactions Requiring Epinephrine First

For severe reactions with respiratory compromise, hypotension, or multi-system involvement:

• Use T78.2XXA for anaphylactic shock
• Use T88.6XXA if the reaction is to a medication 3
• Add secondary codes to identify the causative agent if known (e.g., T36-T50 series for drug-induced reactions) 3

Documentation Requirements

When coding for famotidine use in allergic reactions, ensure documentation includes:

• The specific type of allergic reaction (urticaria, angioedema, anaphylaxis) 4
• Whether epinephrine was administered first (if anaphylaxis) 1
• The severity classification (severe vs. non-severe) 4
• Any comorbid conditions like asthma that increase risk 4

Rare but Important Consideration

Be aware that famotidine itself can rarely cause IgE-mediated anaphylaxis with potential cross-reactivity to other H2 antagonists like ranitidine and nizatidine. 5, 6 If prescribing famotidine for an allergic reaction to another medication, ensure the patient has no history of H2 antagonist allergy.