Zanamivir

The Basics

What is Zanamivir?

Used to treat some types of influenza.

Brand names for Zanamivir

Relenza

How Zanamivir is classified

Antiviral Agents, Neuraminidase Inhibitors

Zanamivir During Pregnancy

Zanamivir pregnancy category

Category CNote that the FDA has deprecated the use of pregnancy categories, so for some medications, this information isn’t available. We still think it’s useful to list historical info, however, given what a common proxy this has been in the past.

What we know about taking Zanamivir while pregnant

There are no adequate and well-controlled studies of zanamivir in pregnant women. Zanamivir should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Embryo/fetal development studies were conducted in rats (dosed from Days 6 to 15 of pregnancy) and rabbits (dosed from Days 7 to 19 of pregnancy) using the same IV doses (1, 9, and 90 mg per kg per day). Pre- and post-natal developmental studies were performed in rats (dosed from Day 16 of pregnancy until litter Day 21 to 23). No malformations, maternal toxicity, or embryotoxicity were observed in pregnant rats or rabbits and their fetuses. Because of insufficient blood sampling timepoints in rat and rabbit reproductive toxicity studies, AUC values were not available. In a subchronic study in rats at the 90-mg-per-kg-per-day IV dose, the AUC values were greater than 300 times the human exposure at the proposed clinical dose. An additional embryo/fetal study, in a different strain of rat, was conducted using subcutaneous administration of zanamivir, 3 times daily, at doses of 1, 9, or 80 mg per kg during Days 7 to 17 of pregnancy. There was an increase in the incidence rates of a variety of minor skeleton alterations and variants in the exposed offspring in this study. Based on AUC measurements, the 80 mg-per-kg dose produced an exposure greater than 1,000 times the human exposure at the proposed clinical dose. However, in most instances, the individual incidence rate of each skeletal alteration or variant remained within the background rates of the historical occurrence in the strain studied. Zanamivir has been shown to cross the placenta in rats and rabbits. In these animals, fetal blood concentrations of zanamivir were significantly lower than zanamivir concentrations in the maternal blood.

Taking Zanamivir While Breastfeeding

What are recommendations for lactation if you're taking Zanamivir?

No information is available on the use of zanamivir during breastfeeding. One group of authors estimated that an exclusively breastfed 5 kg infant would receive about 0.075 mg daily in breastmilk after an inhaled maternal dose of 10 mg, which is less than 1% of the dose in older children. In addition, because zanamivir is poorly absorbed orally, it is not likely to reach the bloodstream of the infant in clinically important amounts.[1]

Maternal / infant drug levels

No information is available on the use of zanamivir during breastfeeding. One group of authors estimated that an exclusively breastfed 5 kg infant would receive about 0.075 mg daily in breastmilk after an inhaled maternal dose of 10 mg, which is less than 1% of the dose in older children. In addition, because zanamivir is poorly absorbed orally, it is not likely to reach the bloodstream of the infant in clinically important amounts.[1]

Possible effects of Zanamivir on milk supply

Relevant published information was not found as of the revision date.

Possible alternatives to Zanamivir

Oseltamivir.