AAN: No Pregnancy Issues in Early Natalizumab Review

TORONTO — An early check of registry data from women with multiple sclerosis who became pregnant while taking natalizumab (Tysabri) does not appear to raise concerns of miscarriages or abnormalities, researchers said here.

“We have to emphasize that these are preliminary findings,” said Lynda Cristiano, MD, medical director of drug safety at Biogen Idec, Cambridge, Mass., who presented data at a poster presentation at the annual meeting of the American Academy of Neurology.

The prospective Tysabri Pregnancy Exposure Registry has enrolled 179 women, of whom 125 have completed outcomes as of Nov. 23, 2009, Cristiano said.

She said 20 miscarriages occurred among those 125 outcomes — about 16%, similar to the estimated 15% rate reported in the general population, according to the March of Dimes. Six other women elected to terminate their pregnancies. No ectopic pregnancies or stillbirths were recorded.

Of the 99 live births, 78 of the pregnancies were full term, Cristiano reported. Eight malformations were reported in six pregnancies — two which involved twin births. The average maternal age in these cases was 29 years.

“As this is an internal and preliminary analysis, birth defects have not yet been classified as major or minor,” she said.

“In addition, the sample size of enrolled patients is small and has limited power to detect an increased risk of major birth defects.” For those reasons, Cristiano said the rate of birth defects was not calculated for her report.

However, she said the cases have no patterns related to the disease-modifying drug.

The registry data reflect the fact that about two-thirds of patients with multiple sclerosis are women, and that the average age of onset of multiple sclerosis coincides with childbearing years. Therefore, disease-modifying agents such as natalizumab are likely to be used by women of childbearing age, Cristiano noted.

Of the 64,600 patients who were exposed to natalizumab through December 2009, about 73% were women, and their average age was 44 years.

“There are no adequate and well-controlled studies of natalizumab in pregnant women,” she said.

Animal studies suggested treatment with natalizumab might have adverse impacts on fetal outcomes.

“Doctors tell their patients who are going on disease modifying therapy that none of these drugs are approved for women who are pregnant,” said Rosalind Kalb, PhD, vice-president of the professional resource center of the New York-based National MS Society.

“This registry and those that were established for the interferon therapies are designed to capture information on outcomes of women who become pregnant by accident while they are taking these drugs,” she explained.

Kalb said registries are the only way to determine safety of these drugs because controlled clinical trials are unlikely to be conducted.

She said the preliminary results presented at AAN do not raise alarms, but don’t prove natalizumab is safe for pregnant women, either.

Primary source: American Academy of Neurology
Source reference:
Cristiano L, et al “Preliminary evaluation of pregnancy outcomes from the TYSABRI (Natalizumab) pregnancy exposure registry” AAN 2010; Abstract P01.185