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Gentamicin in Utero Does Not Cause Hearing Loss


 

MONTEREY, CALIF. — Neonates who were exposed to gentamicin in utero when their mothers were treated for pyelonephritis showed no increased risk of failing screening tests for hearing loss in a controlled study of 284 pregnancies, Dr. Tony Wen said.

The ongoing retrospective chart review analyzed cases of pregnant women who received gentamicin and ampicillin for pyelonephritis and delivered at 32 weeks' gestational age or later with the next gentamicin-free pregnancy matched by gestational age. All neonates underwent otoacoustic emissions testing after birth. Failure or incomplete results brought a second round of otoacoustic emissions testing before discharge. A second failure led to referral for more definitive hearing tests.

Among women with pyelonephritis, 92% received gentamicin, which crosses the placenta at term. Overall, 8% of newborns exposed to gentamicin in utero and 10% of controls failed otoacoustic emissions testing—opposite the trend that investigators expected to see because of concerns about gentamicin's potential effects on hearing, he said at the annual meeting of the Infectious Diseases Society for Obstetrics and Gynecology.

In the general population, 5%–8% of newborns fail otoacoustic emissions tests. The study was inspired by animal studies that found hearing loss in rats exposed in utero to gentamicin.

Gentamicin is an aminoglycoside with broad-spectrum coverage that is commonly used to treat women with pyelonephritis and chorioamnionitis, according to Dr. Wen of the University of Texas, Galveston, and his associates.

A subset analysis by trimester found that early-trimester exposure to gentamicin did not increase risk for otoacoustic emissions testing failure.

Neonates who were small for gestational age showed no increased risk for failing otoacoustic emissions testing from gentamicin exposure.

There was a statistically nonsignificant trend for longer courses of gentamicin to increase the risk for otoacoustic emissions test failure. After 4 days or less of gentamicin treatment, 2% of neonates failed the tests, compared with 12% of neonates whose mothers got gentamicin for 5 days or longer.

“If you have a patient who requires prolonged treatment, once you get the sensitivity testing results, you might consider changing antibiotics” if the mother is on gentamicin, Dr. Wen said.

Women treated with gentamicin and ampicillin received gentamicin in a loading dose of 120 mg followed by 80 mg gentamicin every 8 hours. Patients got 6–20 doses of gentamicin in the study.

The case and control groups did not differ in maternal or gestational age, gravidity, Apgar scores, birth weights, or mode of delivery, among other factors.

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