Is amantadine effective for treating influenza (flu) symptoms?

Amantadine Should NOT Be Used for Flu Symptoms

Amantadine is not recommended for the treatment or prevention of influenza in current clinical practice due to widespread viral resistance, rendering it ineffective against circulating influenza strains. 1

Why Amantadine Is No Longer Recommended

Widespread Resistance Makes It Ineffective

• Resistance rates skyrocketed from 0.4% (1994-1995) to 92% (2005-2006) among influenza A (H3N2) viruses, with resistance remaining persistently high in subsequent seasons 1
• By 2007-2008, approximately 99% of influenza A (H3N2) isolates and 10% of influenza A (H1N1) isolates demonstrated adamantane resistance 1
• The Advisory Committee on Immunization Practices (ACIP) explicitly states that amantadine should not be used for treatment or prevention of influenza until susceptibility is reestablished among circulating viruses 1

Rapid Development of Resistance During Treatment

• Resistant viral strains emerge in approximately one-third of patients during amantadine therapy, often within 2-3 days of starting treatment 1
• A single point mutation in the M2 protein confers complete cross-resistance to both amantadine and rimantadine 1
• Resistant viruses are fully transmissible and pathogenic, creating public health concerns 2

Limited Spectrum of Activity

• Amantadine only works against influenza A viruses and has no activity against influenza B 1, 3
• This limitation is clinically significant since both influenza A and B circulate during flu seasons 1

What Should Be Used Instead

Neuraminidase Inhibitors Are the Current Standard

• Oseltamivir and zanamivir are the recommended antiviral agents for influenza treatment and prophylaxis 1, 4
• These agents are effective against both influenza A and B viruses 1
• When started within 48 hours of symptom onset, neuraminidase inhibitors reduce illness duration by approximately 1 day and decrease complications 1

Clinical Evidence Supporting Current Recommendations

• Oseltamivir reduces overall antibiotic use by 26.7% and influenza-related chest infections requiring antibiotics by 55% 1
• Resistance to neuraminidase inhibitors remains extremely uncommon (<1% of isolates as of 2007) 1
• Prescribing practices changed rapidly after the 2006 CDC recommendation, with adamantane use dropping from 40% to 2% of influenza prescriptions 5

Historical Context (For Understanding Only)

While amantadine was previously effective and FDA-approved for influenza A prophylaxis and treatment 3, historical efficacy data (50-90% prevention, symptom reduction within 24 hours when started within 48 hours) 6 is no longer clinically relevant due to current resistance patterns.

Critical Pitfalls to Avoid

• Do not prescribe amantadine based on older literature or FDA labeling alone—current resistance patterns have rendered it clinically ineffective 1
• Do not use amantadine even in combination therapy unless specifically directed by local health authorities during unusual circumstances with documented susceptibility 1
• Do not delay appropriate neuraminidase inhibitor therapy while considering amantadine as an alternative 1