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Antivirals: Treatment, Prophylaxis and Pandemic Control

Influenza often presents to the primary-care physician several days into an illness that begins with fever, myalgia and cough. Patients, on their own or at the recommendation of their physician, may use paracetamol, aspirin or other non-steroidal anti-inflammatory medications for symptomatic relief. The symptoms of influenza might be regarded by the patient as a bacterial infection and the reason for a visit to the physician is often to obtain a prescription for antibiotics. This and/or inaccurate diagnosis of the disease (see Chapter 5), may lead to over-prescribing of antibiotics for uncomplicated influenza illness, which contributes to the development of microbial resistance to antibiotics. Bacterial complications of influenza generally present 5–7 days after the onset of illness, during a phase of apparent recovery, with subsequent recurrence of symptoms (see Chapter 5).

Clearly, vaccination remains the method of choice for influenza prophylaxis (see Chapter 8). However, under specific conditions – for example, when vaccination has not or cannot be performed, perhaps because of hypersensitivity to egg proteins, or when vaccinated subjects are not fully protected – the use of antiviral drugs should be considered for treatment or prevention of influenza. Antiviral drugs effective against influenza include the M2 channel inhibitors amantadine (Symmetrel®, Lysovir®, Symadine®) and rimantadine (Flumadine®), and the neuraminidase inhibitors (NAIs) zanamivir (Relenza®) and oseltamivir (Tamiflu®). These drugs interfere with specific steps in the replication cycle of influenza virus, either at the level of virus entry or at the level of virus assembly or release from the infected cell.

Since M2 is not present in influenza B or C viruses, the M2 channel inhibitors are active only against influenza A. Their use has been limited by the occurrence of adverse side effects and the risk of induction of drug-resistant viral strains. The NAIs represent a novel class of anti-influenza drugs that are active against influenza A and B viruses; adverse effects are very limited and, thus far, significant development of resistant viral variants has not been reported for these drugs.

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