What are the antiviral medications for influenza?

Antiviral Medications for Influenza

Currently Recommended Antivirals

The primary antiviral agents for influenza are the neuraminidase inhibitors: oseltamivir (oral), zanamivir (inhaled), and peramivir (intravenous), along with the cap-dependent endonuclease inhibitor baloxavir. 1, 2

Neuraminidase Inhibitors (Active Against Influenza A and B)

Oseltamivir (Tamiflu) - Oral formulation

• This is the antiviral drug of choice for influenza management 1, 3
• Available as capsules (30 mg, 45 mg, 75 mg) and liquid suspension 1
• Approved for treatment and chemoprophylaxis in patients ≥1 year 1
• Standard adult dose: 75 mg twice daily for 5 days for treatment; 75 mg once daily for 10 days for prophylaxis 1, 3
• Pediatric dosing is weight-based: 30 mg twice daily for ≤15 kg, 45 mg twice daily for >15-23 kg, 60 mg twice daily for >23-40 kg, 75 mg twice daily for >40 kg 1, 3
• Reduces illness duration by approximately 24 hours when started within 48 hours of symptom onset 3, 4

Zanamivir (Relenza) - Inhaled powder

• Administered via oral inhalation using a specialized device 1
• Dose: 10 mg (2 inhalations) twice daily for 5 days for treatment 1
• Approved for treatment in patients ≥7 years and prophylaxis in patients ≥5 years 1
• Not recommended for patients with underlying airway disease (asthma, COPD) due to risk of bronchospasm 1
• Equally effective alternative to oseltamivir but more difficult to administer 1

Peramivir (Rapivab) - Intravenous formulation

• Single-dose IV administration: 600 mg over 15-30 minutes 5
• Approved for acute uncomplicated influenza in patients ≥2 years who have been symptomatic for ≤2 days 1, 5
• Pediatric dose: 12 mg/kg (maximum 600 mg) for ages 6 months to 12 years 5
• Limited to patients who cannot absorb oral oseltamivir or tolerate inhaled zanamivir 1
• Efficacy in hospitalized patients with serious influenza has not been established 5

Cap-Dependent Endonuclease Inhibitor

Baloxavir - Oral formulation

• Selective inhibitor of influenza cap-dependent endonuclease with activity against influenza A and B 1
• Conditionally recommended for non-severe influenza in high-risk patients 6
• Also conditionally recommended for prophylaxis in exposed asymptomatic persons at very high risk of hospitalization 6

Adamantanes (NOT Currently Recommended)

Amantadine and Rimantadine - Oral formulations

• These medications are NOT recommended for current influenza strains due to widespread resistance 1, 2
• Only active against influenza A (not influenza B) 1
• Circulating H3N2 and H1N1 strains show high resistance rates 1, 2, 3

Critical Treatment Principles

Timing of Initiation

• Maximum benefit occurs when treatment is started within 48 hours of symptom onset 1, 2, 3
• Treatment within 12 hours reduces illness duration by an additional 74.6 hours compared to treatment at 48 hours 7
• For hospitalized patients, initiate treatment immediately regardless of time since symptom onset 2, 3

High-Risk Patients Requiring Immediate Treatment

• Children <2 years and adults ≥65 years 2, 3
• Pregnant and postpartum women 3
• Patients with chronic pulmonary disease, cardiovascular disease, or immunocompromising conditions 1, 2, 3
• Treatment should be offered as early as possible for any hospitalized child or child with severe/complicated illness 1

Duration of Treatment

• Standard treatment duration is 5 days for all neuraminidase inhibitors 1, 3
• Longer courses may be considered for patients who remain severely ill after 5 days or immunocompromised patients 1, 3

Renal Dose Adjustments

• Oseltamivir requires dose reduction for creatinine clearance <30 mL/min: reduce to 75 mg once daily 1, 3, 8
• Peramivir requires dose adjustment for creatinine clearance <50 mL/min 5
• For patients on hemodialysis, administer after dialysis 5

Common Pitfalls to Avoid

• Do not delay treatment while waiting for laboratory confirmation in high-risk patients during influenza season 2, 3
• Do not use zanamivir in patients with asthma or chronic lung disease 1
• Do not use adamantanes (amantadine, rimantadine) for current influenza strains 1, 2, 3
• Taking oseltamivir with food reduces gastrointestinal side effects (nausea/vomiting occur in 10-15% of patients) 3, 7
• Consult CDC surveillance data routinely for current antiviral resistance patterns 1, 2