Anti-influenza agents

Influenza virus strains classification
by core proteins (A, B, or C)
by species of origin (avian, swine)
geographic site of isolation

Anti-influenza drugs approved for use
neuraminidase inhibitors (oral oseltamivir, inhaled zanamivir, IV peramivir)
have activity against both influenza A and influenza B, and there is currently a low level of resistance
adamantanes (amantadine, rimantadine)
have activity against influenza A viruses only, and in recent past seasons there was a high level of resistance (>99%) among both influenza H3N2 and influenza A H1N1

The neuraminidase inhibitors
These agents competitively and reversibly interact with the active enzyme site to inhibit viral neuraminidase activity
Early administration is crucial because replication of influenza virus peaks at 24–72 hours after the onset of illness

Oseltamivir
Orally administered prodrug that is activated by hepatic esterases and widely distributed throughout the body
Potential adverse effects include nausea, vomiting, and headache. Rash is rare
Taking oseltamivir with food does not interfere with absorption and may decrease nausea and vomiting

Zanamivir
Is administered directly to the respiratory tract via inhalation
Of the active compound, 10–20% reaches the lungs; the remainder is deposited in the oropharynx
Potential adverse effects include cough, bronchospasm (occasionally severe), reversible decrease in pulmonary function, and transient nasal and throat discomfort
Zanamivir administration is not recommended for patients with underlying airway disease

Peramivir
A cyclopentane analog
Has activity against both influenza A and B viruses
Is approved as a single 600-mg IV dose for the treatment of acute uncomplicated influenza in adults
The main potential side effect is diarrhea, although serious skin or hypersensitivity reactions (e.g., Stevens-Johnson syndrome, erythema multiforme) have been rarely reported

Amantadine and rimantadine
1-aminoadamantane hydrochloride amantadine and its α-methyl derivative
tricyclic amines of the adamantane family
Mechanisms of Action - block the M2 proton ion channel of the virus particle and inhibit uncoating of the viral RNA within infected host cells, thus preventing its replication
The most common adverse effects are gastrointestinal (nausea, anorexia) and central nervous system (nervousness, difficulty in concentrating, insomnia, light-headedness)