Postexposure chemoprophylaxis is typically administered for a
total of no more than 10 days after the most recent known exposure
to a close contact known to have influenza (105). The likelihood of
compliance and adverse events should be considered when determining
the timing and duration for administering influenza antiviral
medications for chemoprophylaxis. Failure to complete a course
of oseltamivir for chemoprophylaxis because of gastrointestinal
adverse events is common and might lead to antiviral resistance.
In one study, only 15 (48%) of 31 primary school children and
41 (76%) of 54 secondary school children who started oseltamivir
chemoprophylaxis completed a full course. Gastrointestinal adverse
events (e.g., nausea and stomach discomfort) were cited as the most
common reason for stopping medications before the recommended
course was completed (190).
The duration of pre-exposure chemoprophylaxis based on potential
exposure in the community depends on the duration of community
influenza activity. Regimens as long as 28 days for zanamivir, and 42
days for oseltamivir, have been well tolerated, but no published data
are available regarding use of regimens lasting >6 weeks (181). To
be maximally effective as pre-exposure chemoprophylaxis, the drug
must be taken each day for the duration of influenza activity in the
community. During periods of widespread community activity and
limited or no influenza vaccine availability, such as during the 2009
H1N1 pandemic, pre-exposure chemoprophylaxis has a very limited
role because of concerns about antiviral medication supply, need for
long-term use, and the potential for adverse events and selection for
antiviral resistance.
Considerations for Antivi