What is the difference between peramivir iv and other antiviral drugs like zenamivir and oseltamivir

All the above drugs are antivirals and work in the same way by inhibiting viral neuraminidase which reduces viral replication. They are most effective for the treatment of influenza if started within a few hours of the onset of symptoms. They are also used for prophylaxis (prevention) post exposure to influenza. The main difference is the way they are given, peramivir saved for more serious cases.

Oseltamivir is given in the form of a capsule or suspension.
Zanamivir is given as a dry power for inhalation.

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Peramivir is given intravenously only and is reserved for more serious cases where the patient is hospitalized and is either:
1] not responding to either oral or inhaled antiviral therapy,
2] when drug delivery by a route other than an intravenous route is not expected to be dependable or feasible, or
3] for adults only, when the clinician judges IV therapy is appropriate due to other circumstances.
See http://www.drugs.com/fda/peramivir-iv-12622.html
http://www.drugs.com/pro/relenza.html
http://www.drugs.com/oseltamivir.html