Influenza Treatment

Treatment

Initial management of influenza in adults is based on clinical presentation and epidemiological data

Symptomatic Therapy

Fever and Myalgia

May be treated with analgesics (non-opioids) and antipyretics (eg Paracetamol)
Avoid salicylates in children ≤18 years of age because of the risk of Reye’s Syndrome

Cough and Colds

Antivirals for Seasonal Influenza

When used within 48 hours of symptom onset, antiviral agents may reduce the duration of symptoms
- Should not be used if there is uncertainty about diagnosis or if bacterial infection cannot be ruled out
None of the following agents have been shown to be effective in preventing serious influenza-related complications
Data is limited concerning effectiveness of the antiviral agents for the treatment of patients at high-risk of serious complications of influenza

Baloxavir marboxil

The 1st approved influenza virus-specific enzyme polymerase acidic (PA) protein-targeting drug used for the treatment of acute uncomplicated seasonal influenza in patients ≥12 years old who exhibited symptoms for no more than 48 hours
Based on several studies, the therapeutic effect of a single dose of Baloxavir marboxil is comparable to that of the 5-day twice-daily treatment with Oseltamivir

M2 Inhibitors

Eg Amantadine or Rimantadine
Active against influenza A viruses, but not influenza B viruses
There continues to be high resistance to adamantanes among influenza A(H3N2) and influenza A(H1N1) pdm09 viruses
- Thus, Amantadine and Rimantadine are not recommended for treatment and chemoprophylaxis of currently circulating influenza A viruses
Effects:
- As treatment: When used within 48 hours of illness onset in otherwise healthy adults, can reduce duration of uncomplicated influenza
- As chemoprophylaxis: Both drugs are 70-90% effective in preventing illness from influenza A infection
- They prevent illness while allowing subclinical infection and the development of protective antibodies; therapy does not interfere with antibody response to vaccine
- Incidence of CNS side effects is higher among persons taking Amantadine than those taking Rimantadine

Neuraminidase Inhibitors

Eg Oseltamivir, Peramivir, Zanamivir
Oral Oseltamivir and inhaled Zanamivir are used for the treatment and prophylaxis of infection with influenza A or B viruses
IV Peramivir is used for the treatment of influenza A and B viruses especially for those intolerant to oral medications
Combination treatment with neuraminidase inhibitors is not recommended
Effects:
- As treatment: Can reduce duration of uncomplicated influenza A and B illness by approximately 1 day compared with placebo when used within 2 days of illness onset
- Both drugs are effective, 82% Oseltamivir and 84% Zanamivir, in preventing febrile, lab-confirmed influenza illness in otherwise healthy individuals
- As chemoprophylaxis: Experience in preventing spread of influenza within institutions is limited when compared to the M2 inhibitors

Antivirals for Avian Influenza

It is recommended that treatment with a neuraminidase inhibitor is started as early as possible in the clinical course
Data regarding the effectiveness of these antiviral medications against H5N1 infections is limited

Oseltamivir

Primary antiviral agent of choice for the treatment of influenza A(H5N1) and A(H7N9) virus infections
Cultivable virus generally disappears within 2-3 days after initiation of Oseltamivir among avian influenza survivors, although clinical progression has been reported
Standard duration of therapy is 5 days but may be extended to 10 days if with no clinical improvement

Other Neuraminidase Inhibitors

Eg Peramivir, Zanamivir
Highly active in vitro and in animal models, including that due to Oseltamivir-resistant influenza A(H5N1) virus
Orally inhaled Zanamivir has low systemic absorption and may not be useful if extrapulmonary dissemination has occurred; IV Zanamivir may be considered for inpatients with suspected or confirmed resistance to Oseltamivir and Peramivir therapy
Early Amantadine treatment of patients with adamantane-susceptible influenza A(H5N1) virus infections in Hong Kong in 1997 may have been associated with clinical benefit
Zanamivir monotherapy is associated with rapid emergence of resistance
May be used as off-label treatment option in patients with confirmed or strongly suspected infection if Oseltamivir is unavailable especially if the virus is known or likely to be susceptible

M2 Inhibitors (Amantadine, Rimantadine)

Early Amantadine treatment of patients with adamantane-susceptible influenza A(H5N1) virus infections in Hong Kong in 1997 may have been associated with clinical benefit
Not recommended for patients with avian influenza A(H7N9) virus infection
Should only be considered in H5N1 influenza as a treatment option if with treatment failure after neuraminidase inhibitors

Combination Therapy

Combinations of Oseltamivir and M2 inhibitors have enhanced antiviral activity and reduced emergence of resistance
Demonstrated greater antiviral effects and increased survival compared to monotherapy in animal models
Where neuraminidase inhibitors are available:
- In high-risk exposure groups, including pregnant women, Oseltamivir should be administered as chemoprophylaxis continuing for 7-10 days after the last exposure; Zanamivir could be used in the same way as an alternative
- In moderate-risk exposure groups, including pregnant women, Oseltamivir might be administered as chemoprophylaxis continuing for 7-10 days after the last exposure; Zanamivir might be used in the same way
- In low-risk exposure groups and pregnant women, Oseltamivir or Zanamivir should not be administered for chemoprophylaxis
- Amantadine or Rimantadine should not be administered as chemoprophylaxis

Rest is recommended
- Strenuous physical activities (eg running) should be avoided until complete recovery
Patients are advised not to go to work or school and to avoid crowded places to reduce transmission
Return to full activity gradually after illness has resolved, especially if it has been severe
Wear mask in public areas
Cover nose/mouth when coughing or sneezing
Frequent hand washing
Adequate fluid intake is necessary to prevent dehydration
Adequate nutrition will assist in recovery
Advise patient, if necessary, to stop smoking