Influenza Treatment
Principles of Therapy
- Initial management of influenza in adults is based on clinical presentation and epidemiological data
Pharmacotherapy
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 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
Non-Pharmacological Therapy
- 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