What is the recommended treatment for H3N2 influenza?

Treatment of H3N2 Influenza

Oseltamivir (Tamiflu) is the antiviral drug of choice for the treatment of H3N2 influenza, with standard dosing of 75 mg twice daily for 5 days in adults. 1

First-Line Treatment Options

Oseltamivir (Preferred Treatment)

• Adults and adolescents ≥13 years: 75 mg twice daily for 5 days 2
• Children (dosing by weight): 1, 2
  • ≤15 kg: 30 mg twice daily for 5 days

  • 15-23 kg: 45 mg twice daily for 5 days

  • 23-40 kg: 60 mg twice daily for 5 days

  • 40 kg: 75 mg twice daily for 5 days

• Infants and young children:
  • 2 weeks to <1 year: 3 mg/kg twice daily for 5 days 2

Alternative Treatments

• Zanamivir: 10 mg (2 inhalations) twice daily for 5 days for patients ≥7 years without underlying respiratory disease 1
• Peramivir: Single IV dose for patients ≥6 months who cannot take oral medication 1
• Baloxavir: Single oral dose based on weight for patients ≥12 years 1

Treatment Timing and Indications

Treatment should be initiated as soon as possible after symptom onset, ideally within 48 hours, as earlier treatment provides better clinical responses 1, 3. Studies show that starting treatment within the first 12 hours after fever onset can reduce illness duration by 74.6 hours (3.1 days) compared to starting at 48 hours 3.

Treatment should be offered regardless of vaccination status for: 1

1. Any hospitalized patient with suspected or confirmed influenza
2. Patients with severe, complicated, or progressive illness
3. Patients at high risk for influenza complications, including:
   • Children <5 years (especially <2 years)
   • Adults ≥65 years
   • Persons with chronic medical conditions
   • Immunocompromised individuals
   • Pregnant women

Efficacy and Benefits

Oseltamivir treatment reduces:

• Duration of illness by approximately 29-35 hours (25-30%) in adults 4
• Risk of secondary complications requiring antibiotics 5
• Duration of viral shedding 1
• Symptom severity and improves quality of life measures 4

Important Considerations

Resistance Patterns

High levels of resistance to adamantanes (amantadine and rimantadine) exist among influenza A (H3N2) strains, so these drugs should not be used 1, 6. Neuraminidase inhibitors (oseltamivir, zanamivir) generally maintain effectiveness against H3N2 strains 1.

Side Effects

• Oseltamivir: Primarily gastrointestinal (nausea, vomiting) which can be minimized by taking with food 5
• Zanamivir: Not recommended for patients with underlying airway disease due to risk of bronchospasm 1

Special Populations

• Renal impairment: Dose adjustment required for oseltamivir in patients with creatinine clearance <60 mL/min 6
• Immunocompromised patients: May require longer treatment courses (up to 10 days) 6

Prevention Strategies

While treatment is important, prevention remains crucial:

• Annual influenza vaccination (though effectiveness against H3N2 is often lower at 26-50%) 6
• Good hand hygiene and respiratory etiquette
• Post-exposure prophylaxis with oseltamivir may be considered for high-risk contacts 1

Remember that clinical benefit is greatest when treatment is started early, but benefits may still be observed when treatment is initiated after 48 hours in severely ill or high-risk patients 6.