Zanamivir

The concurrent use of RELENZA with live attenuated influenza vaccine (LAIV) intranasal has not been evaluated. However, because of potential interference between these products, LAIV should not be administered within 2 weeks before or 48 hours after administration of RELENZA, unless medically indicated. The concern about possible interference arises from the potential for antiviral drugs to inhibit replication of live vaccine virus. Trivalent inactivated influenza vaccine can be administered at any time relative to use of RELENZA [see Microbiology ( 12.4 )] . Live attenuated influenza vaccine, intranasal ( 7 ): • Do not administer until 48 hours following cessation of RELENZA.

• Do not administer RELENZA until 2 weeks following administration of the live attenuated influenza vaccine, unless medically indicated.

8.1 Pregnancy Risk Summary Available data from published studies suggest that use of RELENZA during pregnancy is not associated with an increased risk of birth defects or adverse maternal or fetal outcomes. However, these studies are limited by their small sample sizes, which preclude a definitive assessment of the risk (see Data). There are risks to the mother and fetus associated with influenza infection in pregnancy (see Clinical Considerations) .

In animal reproduction studies, no adverse developmental effects were observed with intravenous or subcutaneous administration of zanamivir at exposures 300 and 150 times, respectively, the systemic exposure at the maximum recommended human inhalation dose (MRHID) of 10 mg twice daily (see Data) . The background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively.

Clinical Considerations Disease-Associated Maternal and/or Embryo/Fetal Risk: Pregnant women are at higher risk of severe complications from influenza, which may lead to adverse pregnancy and/or fetal outcomes, including maternal death, stillbirths, birth defects, preterm delivery, low birth weight, and small for gestational age. Data Human Data: A study of population-based registers from Denmark, Norway, Sweden, and France reported outcomes of 5,824 pregnant women who filled a prescription for an NAI compared with outcomes in unexposed pregnant women in the general population. This study included 1,560 women who filled a prescription for zanamivir (including 321 first trimester exposures).

Although no specific analyses were conducted for zanamivir, exposure to the NAI class in utero was not associated with major birth defects, preterm birth, low birth weight, small for gestational age, still birth, neonatal morbidity, or neonatal mortality. A few published studies compared outcomes of pregnant women exposed to zanamivir with outcomes in various comparator cohorts. These studies suggested no increased risk of major birth defects, preterm birth, or low birth weight. Sample sizes in these studies ranged from 50 to 180 pregnant women exposed to zanamivir, including 15 to 44 women exposed in the first trimester.

Limitations of available studies include the lack of specific analyses for zanamivir, possible exposure and outcome misclassification, and small sample…

8.2 Lactation Risk Summary There are no data on the presence of zanamivir in human milk or the effects on milk production. There are data from adults that have shown low oral bioavailability of zanamivir. Limited data from postmarketing case reports have not suggested a safety concern in infants exposed to breast milk of mothers using RELENZA. Zanamivir was present in the milk of lactating rats without effect on nursing pups (see Data) . The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for RELENZA and any potential adverse effects on the breastfed child from RELENZA or the underlying maternal condition.

Data In a lactation study, zanamivir was excreted in the milk of lactating rats administered zanamivir intravenously (10 mg/kg) on post-partum/lactation Day 10, with peak milk concentrations of approximately 10% that of maternal plasma concentrations occurring 30 minutes post-dose. No effects of zanamivir on growth and postnatal development were observed in nursing pups at the highest intravenous dose tested in rats. Maternal systemic exposure (AUC) of zanamivir was approximately 300 times the exposure in humans at the MRHID.