What interventions are recommended for an elderly patient with impaired renal function and a history of comorbidities, experiencing an allergic reaction to Tamiflu (oseltamivir) characterized by itching and redness on the neck?

Management of Allergic Reaction to Tamiflu (Oseltamivir)

Immediately discontinue oseltamivir and administer oral antihistamines for this mild cutaneous allergic reaction characterized by itching and redness on the neck. 1

Immediate Interventions

Discontinue the Offending Drug

• Stop oseltamivir immediately upon recognition of the allergic reaction, as avoidance or discontinuation is the most effective management strategy for drug allergy 2
• Do not administer any further doses while symptoms persist 2

Treat the Allergic Reaction

• Administer oral antihistamines (such as diphenhydramine or cetirizine) as first-line treatment for mild cutaneous reactions with pruritus and erythema 1
• Second-generation antihistamines (loratadine, desloratadine, cetirizine, or fexofenadine) are preferred in elderly patients to minimize sedation and impairment 3
• Parenteral antihistamines via intramuscular or intravenous injection can be used if oral administration is not feasible 1

Monitor for Progression

• Obtain vital signs as soon as symptoms are noted to assess for systemic involvement 1
• Observe the patient for 30-60 minutes after symptom resolution to ensure no progression to more severe reactions 1
• Watch for signs of anaphylaxis including hypotension, respiratory symptoms, or repetitive emesis, which would require immediate intramuscular epinephrine 1

Additional Supportive Measures

Symptomatic Relief

• Topical corticosteroids can be applied to areas of redness and itching to reduce local inflammation 2
• Acetaminophen (650-1000 mg every 6 hours) may be used for any associated discomfort, with standard dosing appropriate given the patient's renal function (GFR 47 mL/min is not severe enough to require dose adjustment) 4

Documentation and Future Prevention

• Document the allergic reaction clearly in the medical record as a drug allergy 2
• Counsel the patient to avoid oseltamivir in the future 2
• Provide the patient with written documentation of this allergy 2

Alternative Antiviral Therapy

If Influenza Treatment Still Required

• Zanamivir (inhaled) 10 mg (two inhalations) twice daily is the preferred alternative, as it has an unrelated chemical structure and requires no dose adjustment for renal impairment 4
• Zanamivir can be used at standard dosing without concern for the patient's creatinine clearance of 47 mL/min 4
• Ensure the patient does not have underlying airway disease (asthma or COPD) before prescribing zanamivir, as bronchospasm is a contraindication 1

Critical Considerations for This Elderly Patient

Renal Function Context

• While this patient has impaired renal function (GFR 47 mL/min), the allergic reaction takes precedence over dosing adjustments 4, 5
• Had the patient tolerated oseltamivir, the appropriate dose would have been 75 mg twice daily, as dose reduction is only mandatory when creatinine clearance falls below 30 mL/min 4, 5

Common Pitfalls to Avoid

• Do not confuse gastrointestinal side effects with allergic reactions: nausea and vomiting are common adverse effects occurring in 10% of patients but are not allergic in nature 6
• Do not restart oseltamivir after symptom resolution, as this represents a true drug allergy requiring permanent avoidance 2
• Do not delay treatment of the allergic reaction while obtaining vital signs if the reaction appears severe 1

When to Escalate Care

• If the patient develops throat tightness, difficulty breathing, hypotension, or angioedema, administer intramuscular epinephrine immediately (0.3-0.5 mg for adults) and consider transfer to an emergency department 1
• Isolated subjective symptoms like throat itching may represent a prodromal phase of a more severe reaction and warrant close observation 1