Influenza 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

• May be treated with cough and cold preparations (eg expectorants, mucolytics)

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 w/ 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 & B viruses especially for those intolerant to oral medications
• Combination treatment w/ 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 & 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) & 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 w/ suspected or confirmed resistance to Oseltamivir & 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 w/ adamantane-susceptible influenza A(H5N1) virus infections in Hong Kong in 1997 may have been associated w/ clinical benefit
• Not recommended for patients w/ avian influenza A(H7N9) virus infection
• Should only be considered in H5N1 influenza as a treatment option if w/ 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 & 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