influenza
INFLUENZA
The clinical spectrum of influenza ranges from asymptomatic infection to primary viral pneumonia that may progress to death.
Patients presenting with influenza-like illness (ie temperature of 37.8ºC, cough and/or sore throat and absence of a known cause other than influenza) might be infected with different types of influenza virus [eg avian influenza (H5N1)] as well as other respiratory pathogens.
A high index of suspicion is needed to recognize influenza in hospitalized patients.
Pneumonia is the most common complication of influenza virus.

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

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 or Zanamivir
  • Used for treatment and prophylaxis of infection with influenza A or B viruses
  • Effects:
    • As treatment: Can reduce duration of uncomplicated influenza A and B illness by approx 1 day compared with placebo when used within 2 days of illness onset
    • Both drugs are effective, 82% (Oseltamivir) or 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) 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

Peramivir

  • Newly approved neuraminidase inhibitor for highly pathogenic avian influenza virus A/Vietnam/UT3040/2004 (H5N1)
  • An intravenous (IV) neuraminidase inhibitor given as a single dose
  • Intended for patients ≥18 years who have uncomplicated influenza and shown symptoms of flu for no >2 days

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
  • 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
  • Monotherapy is associated with rapid emergence of resistance
  • May be used as 2nd-line therapy in patients with confirmed or strongly suspected infection if neuraminidase inhibitors are unavailable especially if the virus is known or likely to be susceptible

Combination Therapy

  • Combinations of Oseltamivir and M2 inhibitors (Amantadine or Rimantadine) have enhanced antiviral activity and reduced emergence of resistance
  • Demonstrated greater antiviral effects and increased survival compared to monotherapy in animal models

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
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