Long-acting Neuraminidase Inhibitor Laninamivir Octanoate as Post-exposure Prophylaxis for Influenza

Close contact with an influenza patient increases the risk of subsequent infection. In such cases, antiviral chemoprophylaxis should be considered for persons at high risk from serious illness or death related to influenza (the elderly, those with chronic respiratory illness or metabolic disorders including diabetes mellitus, chronic heart disease, and immunodeficiency) [1, 2]. A single administration of laninamivir octanoate, a long-acting neuraminidase inhibitor, has been demonstrated to be an effective treatment for influenza [3–5], while oseltamivir and zanamivir need repeated administration, twice daily for 5 days. In Japan, laninamivir octanoate has been used widely not only because of its high level of efficacy and safety but also because of its convenience [6–8]. For the post-exposure prophylaxis of influenza, the inhalation of 20 mg of laninamivir octanoate once daily for 2 or 3 days effectively prevented the development of influenza through household contacts in a study conducted during the 2011–2012 influenza season [9]. However, it was not demonstrated that a single inhalation of laninamivir octanoate was effective for post-exposure prophylaxis. In a study conducted during the 2009 influenza pandemic season, the inhalation of 20 or 40 mg of laninamivir octanoate once a week reduced the proportion of patients who developed influenza (relative risk reduction [RRR] compared with placebo, 45.8% and 43.2%, respectively), but the differences with placebo were not significant [10]. A pharmacokinetics finding that a relatively high laninamivir concentration persisted in the lungs for 10 days after a single inhalation [11] suggested that a single inhalation of laninamivir octanoate may be effective for post-exposure prophylaxis. This study was conducted to evaluate the efficacy of a single inhalation of 40 mg of laninamivir octanoate as post-exposure prophylaxis for household contacts.