New Flu Therapy on the Horizon
ABSTRACT & COMMENTARY
Source: Hayden FG, et al. Efficacy and safety of the neuraminidase inhibitor zanamivir in the treatment of influenzavirus infections. N Engl J Med 1997;337:874-880.
Annual influenza epidemics represent a signi-ficant health and economic burden worldwide. Current strategies to control the disease include annual influenza vaccinations developed based upon the previous year’s epidemic-ending strains and prophylaxis or treatment using amantadine or rimantadine, both of which are effective only against influenza A. Since influenza B causes approximately 35% of cases overall, expanded therapeutic regimens could serve to alleviate symptoms and save lives in a significant number of patients.1
Hayden and colleagues examined the efficacy of topically applied zanamivir, a neuraminidase inhibitor effective against both influenza A and B viruses, in a multicenter, randomized, double-blind, placebo-controlled study of adults with naturally acquired influenza-like illness of less than 48 hours’ duration. Intranasal and inhaled forms of zanamivir were used. Patients were randomized to one of three groups: zanamivir 10 mg by inhalation plus zanamivir 6.4 mg intranasally; zanamivir 10 mg by inhalation plus placebo intranasally; or placebo by inhalation and intranasally. Twice daily administration lasted for five days. A total of 417 patients with suspected influenza were randomized to one of the above treatment arms. Confirmed influenzavirus infection was present in 262 patients (63%), 56% due to influenza A and 44% due to influenza B. Median time to relief of symptoms was significantly shorter in both zanamivir groups (four days) compared to placebo (five days). In those patients treated within 30 hours of symptom onset and those patients febrile upon entry into the study, the positive effects of zanamivir were even more impressive, with alleviation of symptoms three days sooner when compared to placebo (P £ 0.001). Hayden et al conclude that topical administration of zanamivir in naturally acquired influenzavirus infection has clinically significant benefits comparable to studies evaluating amantadine and rimantadine and is effective against both influenza A and B illness, especially when administered early in the course of illness.
COMMENT BY FREDERIC KAUFFMAN, MD, FACEP
Influenza affects patients of all age groups, but the elderly and those with chronic illnesses are most susceptible to complications and death. The current vaccination practice is effective in only 70-90% of recipients, with even less efficacy in the elderly. In addition, current treatment with either amantadine or rimantadine is effective only against influenza A. Hayden et al previously demonstrated that zanamivir is effective in experimentally induced human influenza infection. The current study lends support to the possibility of expanded coverage to include naturally occuring influenza B. One must be careful, however, in accepting comparison of zanamivir with current regimens using historical controls. The final step in the evaluation of a potential role for zanamivir must include a blinded, randomized comparison of amantadine and/or rimantadine vs. zanamivir in naturally occuring influenza A and B infection.
Reference
1. Couch RB. A new antiviral agent for influenza: Is there a clinical niche? N Engl J Med 1997;337:927-928.
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