Effect Measure

Patient A. On April 15, a woman aged 33 years at 35 weeks' gestation with a 1-day history of myalgias, dry cough, and low-grade fever was examined by her obstetrician-gynecologist. She had been in relatively good health and had been taking no medications other than prenatal vitamins, although she had a history of psoriasis and mild asthma. The patient had not recently traveled to Mexico. Rapid influenza diagnostic testing performed in the physician's office was positive.

On April 19, she was examined in a local emergency department, with worsening shortness of breath, fever, and productive cough. She experienced severe respiratory distress, with an oxygen saturation of approximately 80% on room air and a respiratory rate of approximately 30 breaths per minute. A chest radiograph revealed bilateral nodular infiltrates. The patient required intubation and was placed on mechanical ventilation. On April 19, an emergency cesarean delivery was performed, resulting in a female infant with Apgar scores of 4 at 1 minute after birth and of 6 at 5 minutes after birth; the infant is healthy and has been discharged home. On April 21, the patient developed acute respiratory distress syndrome (ARDS). The patient began receiving oseltamivir on April 28. She also received broad-spectrum antibiotics and remained on mechanical ventilation. The patient died on May 4.

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Patient C. On April 29, a woman aged 29 years at 23 weeks' gestation was experiencing cough, sore throat, chills, subjective fever, and weakness of 1 day's duration and was seen at the family practice clinic where she had been receiving prenatal care. The patient had a history of asthma but was not taking any asthma medications. Her son, aged 10 years, reportedly had similar symptoms the week before the onset of her symptoms. Another son, aged 7 years, had become ill on the same day as his mother and accompanied her to the clinic. At the clinic, the younger son was coughing vigorously and was asked to put on a mask by office staff members. Rapid influenza diagnostic testing in the family practice clinic of a nasopharyngeal sample from patient C was positive. The woman was prescribed oseltamivir, which she began taking later the same day. Her symptoms are resolving without complications, and her pregnancy is proceeding normally. (CDC, Morbidity and Mortality Weekly Report [MMWR])

Patient C's obstetrician was also pregant (13 weeks) and she was started on oseltamivir immediately. So far the swine flu virus is sensitive to the neuriminidase inhibitor antivirals, oseltamivir (Tamiflu) and zanamivir (Relenza), but oseltamivir is recommended for pregnant women because it is absorbed systemically. The oseltamivir tablet is not the active form of the drug but a "pro-drug" designed to be absorbed in the gastrointestinal tract. Once in the blood it is converted to the active form by enzymes in the liver. Zanamivir is already in the active form but cannot be absorbed. It is administered with an inhaler, so only affects virus in the respiratory tract. CDC believes it is preferable to get the drug to other organs, including the placenta.

Do we know that oseltamivir is safe for the fetus? No good safety studies have been done, but what evidence exists does not suggest risk to the fetus. Given the risk of influenza, CDC believes the risk-benefit balance nets out in favor of 5 days of oseltamivir use in pregnant women as early in their illness as possible.