antibioticsbooks

216 PART 5 Antiviral Drugs
Adverse Effects
Both oseltamivir and zanamivir are well-tolerated
drugs. Oseltamivir can cause nausea, vomiting,
and abdominal pain, but these tend to be transient
effects. Headache and fatigue can also occur, particularly
during prophylactic use when the drug
is given for a longer period of time. Zanamivir has
mostly pulmonary adverse effects, including cough
and bronchospasm. Avoid using it in patients with
asthma or other reactive pulmonary diseases.
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Important Facts
• Neuraminidase inhibitors are most effective
when started early in the course of infection,
because viral replication peaks early (48–72
hours after infection). The package inserts for
these drugs state they should be started in
patients who have been symptomatic for no
more than two days and should be given for
five days, but clinicians do not always follow
these guidelines. In severe influenza infections
such as those that require hospitalization or in
vulnerable patients, it may be worth extending
the duration of treatment.
• Resistance to the neuraminidase inhibitors can
occur. Their utility is dictated by the degree of
resistance that exists in the dominant influenza
strains of the season. Currently, zanamivir is
active against the vast majority of oseltamivirresistant
strains, but these resistance patterns
may change.
• Both of these drugs are highly effective at preventing
influenza infection when the predominant
strains in the community are susceptible,