Purpose: To assess the effect of neuraminidase inhibitor (NI), zanamivir, on pregnancy outcomes.
Methods: The Health Improvement Network (THIN) provided data from UK General Practitioners (GPs) for 144 pregnant women who were prescribed zanamivir and 144 age- and date-matched untreated comparators with no recorded diagnosis of influenza. Groups were assessed for baseline characteristics, treatment-emergent diagnoses in the mother, pregnancy outcomes and congenital malformations diagnosed in the offspring within 28 days of birth.
Results: Treatment and comparator groups were similar at baseline. Most (100/144) zanamivir prescriptions occurred during the second and third trimesters. Groups were similar in recorded smoking during pregnancy; more women in the comparator group had recorded alcohol use. The zanamivir group had more diagnoses compatible with influenza-like illness (ILI) and was more often prescribed antibiotics, analgesics and medicines for respiratory and gastrointestinal symptoms. Pregnancy outcomes other than live birth were not found in the GP record, possibly due in part to cohort entry having occurred late in most pregnancies. There was no difference between groups in the risk of any treatment-emergent diagnosis. Congenital anomalies occurred in similar proportions, but infants born to zanamivir-exposed women had substantially fewer diagnoses from the cluster of cardiac defects consisting of atrial and ventricular septal defects and patent ductus arteriosus (1 zanamivir, 6 comparators).
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