Management of Adult Patient with Confirmed Influenza
Immediate Antiviral Treatment
Initiate oseltamivir 75 mg orally twice daily for 5 days as soon as possible, ideally within 48 hours of symptom onset 1. Treatment reduces illness duration by approximately 1.3 days and decreases the severity of symptoms by up to 38% compared to placebo 1, 2.
Key Treatment Principles
Start treatment immediately without waiting for laboratory confirmation if clinical suspicion is high, as early initiation (within 24 hours) provides the greatest benefit 3
Take oseltamivir with food to reduce nausea, which occurs in approximately 10-15% of patients 1, 2
Continue treatment for the full 5-day course even if symptoms improve earlier 1
Extended Treatment Window for High-Risk Patients
Treatment beyond 48 hours should still be offered to patients who are severely ill, hospitalized, or at high risk of complications 4, 5. This includes:
- Patients requiring hospitalization for influenza 5
- Adults ≥65 years of age 6, 7
- Patients with chronic cardiac or pulmonary disease 4, 1
- Immunocompromised individuals 5
- Pregnant women 5
The evidence base for treatment beyond 48 hours is limited, as most trials enrolled patients within 36-48 hours of symptom onset, but severely ill patients may still benefit from late treatment based on viral replication patterns 5.
Dose Adjustments
- Reduce dose to 75 mg once daily if creatinine clearance is <30 mL/min 5, 1
- Oseltamivir is not recommended for end-stage renal disease patients not on dialysis 1
Antibiotic Considerations
Do NOT routinely prescribe antibiotics for uncomplicated influenza in previously healthy adults 4, 5. Antibiotics are only indicated when:
- Bacterial superinfection is suspected, particularly with worsening symptoms after initial improvement, recrudescent fever, or increasing breathlessness 6, 5
- Clinical or radiographic evidence of pneumonia develops 6, 5
- Patient has severe pre-existing COPD or other chronic respiratory disease 5
First-Line Antibiotic Choices When Indicated
- Co-amoxiclav (amoxicillin-clavulanate), doxycycline, or cefuroxime to cover Streptococcus pneumoniae, Staphylococcus aureus, and Haemophilus influenzae 4, 6, 5
- Administer within 4 hours if pneumonia is confirmed on hospital admission 6
Monitoring and Red Flags
Instruct the patient to seek immediate medical attention if any of the following develop 6, 7:
- Persistent high fever beyond 3 days 6
- Increasing shortness of breath or respiratory rate >24/min 6
- Chest pain or blood-tinged sputum 6
- Confusion or altered mental status 6, 7
- Inability to maintain oral intake or signs of dehydration 6
- Oxygen saturation <90% 6
Hospitalization Criteria
Consider hospitalization if ≥2 of the following are present at day 6 6:
- Temperature >37.8°C (100°F)
- Heart rate >100/min
- Respiratory rate >24/min
- Systolic blood pressure <90 mmHg
- Oxygen saturation <90%
- Inability to maintain oral intake
- Altered mental status
Symptomatic Management
- Acetaminophen or ibuprofen for fever, headache, and myalgias 7
- Encourage adequate oral fluid intake to prevent dehydration 7
- Rest to reduce metabolic demands 7
Common Pitfalls to Avoid
Do not withhold oseltamivir based solely on time from symptom onset in high-risk or severely ill patients, as they may still benefit from treatment beyond 48 hours 4, 5
Do not prescribe antibiotics prophylactically without evidence of bacterial infection, as this promotes resistance without proven benefit 5, 7
Do not assume absence of fever rules out severe influenza, particularly in elderly patients who may not mount adequate febrile responses 7
Vomiting is the most common adverse effect of oseltamivir (15% vs 9% placebo), but it is typically mild and transient, especially when taken with food 4, 1, 2
Alternative Antiviral Options
Zanamivir (inhaled) or baloxavir (single oral dose) may be considered as alternatives to oseltamivir, though oseltamivir remains first-line due to oral administration and established efficacy 4, 8
Zanamivir carries a risk of life-threatening bronchospasm and should be avoided in patients with underlying respiratory disease 9, 10