New research suggests that women who receive antibiotics during labor may be getting more than the necessary dosage.

Ohio State researchers found that up to a quarter of the estimated 4 million women who receive an antibiotic during labor in order to protect their infants from developing a serious infection may be getting five times the necessary dose of medication.

David Colombo, assistant professor of obstetrics and gynecology at OSU and one of the authors of the study, found that the high dosage of penicillin pregnant patients were receiving may not be needed.

“Physicians may be using too much penicillin,” said Colombo. “There is a shortage of this type of penicillin – the kind that is given intravenously.”

Researchers were also concerned that the overuse of antibiotics overall would lead to the increased resistance of harmful bacteria to these drugs.

Penicillin is the most common antibiotic given to a woman at risk of transferring the bacteria group B Streptococcus (GBS) to her newborn. GBS is a type of bacterium that causes illness in newborn babies and the most common cause of life-threatening infections in infants such as pneumonia, meningitis and sepsis, a sometimes-fatal blood infection.

Transfer of GBS, through either the vagina or rectum, becomes important at the time of labor and delivery – when antibiotics are effective in preventing the spread of GBS from mother to baby. Giving certain pregnant women antibiotics, such as penicillin, through the vein during labor can prevent most GBS disease in newborns.

The Centers for Disease Control and Prevention recommend that infected women receive about 3 grams of penicillin (5 million units) when labor begins, followed by 1.5 grams (2.5 million units) every four hours until delivery. But a dose of about 0.5 grams (1 million units) given initially and again every four to six hours until delivery may give the same protective effect, said Colombo.

For their study, researchers surveyed fifteen healthy pregnant women in their third trimester of pregnancy, but who were not yet in labor. Each of these women was given one 0.5-gram dose of intravenous penicillin. The researchers wanted to analyze the concentration of penicillin in each woman’s blood, so they took blood samples through a catheter at one, five and 30 minutes after the initial dose and then once every 30 minutes for a total of 4 hours.

Colombo, along with the College of Medicine and Public Health researchers Jeffrey Johnson, Debra Gardner and Cynthia Shellhass, found that this lower dosage of penicillin is excreted from the body at the same rate as does the 3- and 1.5-gram doses, suggesting that a lower dosage of penicillin provides levels sufficient enough to protect a newborn from infection caused by GBS.

“By administering penicillin to the mother, the baby is actually being treated,” said Colombo. “We can give the 0.5-gram doses of penicillin to mothers in labor and get the same beneficial results as we do with the larger doses.”

“When the new recommendations come out (regarding the amount of intravenous penicillin women in labor should be given), we hope that these results will be taken into consideration,” said Colombo.

Kimberly Haskins, a labor and delivery nurse at OSU Maternity Center, said that penicillin is effective at preventing GBS disease in the newborn and is generally safer when treated during labor.

“When mothers are treated during pregnancy, they may be exposed to penicillin-resistant strains of other bacteria and the recurrence rate is high,” she said.

Obstetricians at the OSU Maternity Center administer a 2 gram dose of ampicillin to women in labor and then 1 gram every four hours until delivery. They have found that this amount sufficiently protects the newborn from infection.

Kathy Hayes, an expectant mother, was unaware of the concerns regarding penicillin and labor.

“I had no idea that a smaller dosage was as effective as a larger one. I assumed that all women with GBS were given the same amount of penicillin during labor. If I carry GBS, it will be interesting to find how much penicillin I am given and why,” she said.

Pregnant women who have a higher risk for GBS disease are those who have had a previous baby with GBS, experience labor or rupture of membranes before 37 weeks, or have labor or encounter a rupture of membranes 18 hours or more before delivery.

Expectant women who carry GBS should be offered antibiotics at the time of labor or membrane rupture. “Because women who carry GBS but don’t develop complications, such as developing a fever during labor, have a relatively low risk of delivering a baby with the disease, the decision to take antibiotics during labor should balance both the risks and benefits,” said Haskins.

Eunsun Cho and Patty Fan-Havard, both in the College of Pharmacy also partook in the study.

Useful Linkswww.cdc.gov – Centers for Disease Control and Prevention www.astdhpphe.org/infect/strepb.html – Site provides facts about group B Streptococcus (GBS) www.osumedcenter.edu – OSU Maternity Centermedicine.osu.edu -OSU College of Medicine and Public Healthwww.pharmacy.ohio-state.edu – OSU College of Pharmacy