Treatment of Influenza in Adults
Adults with influenza should receive oseltamivir 75 mg orally twice daily for 5 days, initiated within 48 hours of symptom onset. 1, 2
Primary Treatment Recommendations
Antiviral Therapy Selection
Oseltamivir (75 mg twice daily for 5 days) is the preferred first-line treatment for adults with uncomplicated influenza A or B infection 1, 2
Zanamivir (10 mg [2 inhalations of 5 mg] twice daily for 5 days) is an alternative option for adults, but is contraindicated in patients with underlying airways disease such as asthma or chronic obstructive pulmonary disease 1
Both medications are FDA-approved for treatment of influenza A and B in adults 1, 2
Critical Timing Considerations
Treatment must be initiated within 48 hours of symptom onset to achieve maximum clinical benefit 1, 3, 2
Earlier initiation provides greater benefit: treatment within 12 hours reduces illness duration by an additional 74.6 hours compared to treatment at 48 hours, and treatment within 24 hours provides an additional 53.9 hours of benefit 4
Oseltamivir reduces median time to improvement by approximately 1.3 days (29-35 hours) compared to placebo when started within 36-40 hours of symptom onset 2, 5
Special Populations and Extended Treatment
Hospitalized and Severely Ill Patients
Continue oseltamivir 75 mg twice daily for 5 days even beyond the 48-hour window in hospitalized patients who are severely ill or have underlying conditions 1, 6
Longer treatment regimens may be necessary in severely ill hospitalized patients or persons with immunosuppression 1
In immunocompromised patients, prophylactic dosing may be continued for up to 12 weeks 2
Patients with Renal Impairment
Reduce oseltamivir dose by 50% to 75 mg once daily if creatinine clearance is less than 30 mL/minute 6, 2
No dose adjustment is required for zanamivir in patients with renal impairment, as limited data suggest it is well tolerated even with severe renal dysfunction 1
Elderly Patients (≥65 Years)
No dose reduction is recommended based on age alone for either oseltamivir or zanamivir 1
Elderly patients remain eligible for antiviral treatment even without documented fever, particularly those with dementia or delirium who may not mount an adequate febrile response 6
Patients with Chronic Cardiac or Respiratory Disease
Patients with COPD and influenza should receive antibiotics even without confirmed pneumonia, as they are at high risk for bacterial complications and secondary infections 6
First-line oral antibiotic options include co-amoxiclav or doxycycline; if IV therapy is required, use co-amoxiclav or a second/third generation cephalosporin such as cefuroxime or cefotaxime 6
Oseltamivir significantly reduces the median duration of acute febrile illness in patients with cardiac disease (44.0 vs 64.7 hours, p=0.026) and chronic obstructive airways disease (37.9 vs 53.8 hours, p=0.004) 7
Clinical Benefits and Outcomes
Symptom Resolution
Oseltamivir reduces illness duration by 19-30% (median reduction of 29-35 hours) compared to placebo 2, 5, 7
The medication reduces severity of illness by up to 38% when initiated within 36 hours of symptom onset 8
Specific symptom improvements include: fatigue reduced by 29%, myalgia by 26%, and 57% fewer patients remain febrile at 48 hours compared to placebo 7
Prevention of Complications
Oseltamivir significantly reduces the incidence of secondary complications including otitis media, bronchitis, pneumonia, and sinusitis 8, 4
The use of antibacterials is reduced significantly in oseltamivir recipients 8
Administration and Tolerability
Dosing Instructions
Oseltamivir may be taken with or without food; however, tolerability is enhanced when taken with food 2, 4
The oral suspension formulation (6 mg/mL) is preferred for patients who cannot swallow capsules 2
Adverse Effects
Nausea and vomiting are the most commonly reported adverse events, occurring in approximately 10% of patients 8, 4
Gastrointestinal events are typically mild, transient, and resolve within 1-2 days 8, 4
Both nausea and vomiting are less likely when oseltamivir is taken with food 8
The medication is generally well tolerated with transient gastrointestinal effects observed in one in seven oseltamivir-treated patients compared with one in 12 patients on placebo 7
Critical Pitfalls to Avoid
Do not withhold antibiotics in COPD patients with influenza, as this population requires antibiotic coverage even without confirmed pneumonia 6
Do not use corticosteroids for influenza pneumonia, as they are associated with increased mortality, unless there is a specific indication like severe COPD exacerbation requiring steroids 6
Do not stop oseltamivir early; complete the full 5-day course even if symptoms improve 1, 6
Do not delay treatment waiting for laboratory confirmation; initiate therapy based on clinical presentation during influenza season 3
Monitoring Requirements
Monitor vital signs at least twice daily including temperature, respiratory rate, pulse, blood pressure, mental status, and oxygen saturation 3, 6
Watch for clinical deterioration including worsening shortness of breath, recrudescent fever, respiratory rate >24/min, oxygen saturation <90%, inability to maintain oral intake, and worsening mental status or delirium 6
Provide supplemental oxygen if oxygen saturation falls below 90% 3
Resistance Considerations
Oseltamivir resistance has rarely been observed and appears to be of no clinical relevance due to reduced transmissibility and pathogenicity of resistant mutants 4
To limit potential transmission of antiviral drug-resistant influenza virus during outbreaks, reduce contact between persons taking antiviral drugs for treatment and others, including those taking chemoprophylaxis 1