NEW YORK (Reuters Health) – As a tocolytic agent to aid external cephalic version, the calcium antagonist nifedipine doesn’t seem to work very well, according to a systematic review of three relevant clinical trials.

“Our review provides evidence that nifedipine is less effective than terbutaline (a betamimetic) in facilitating external cephalic version,” Dr. Natasha Nassar from University of Sydney in Australia, noted in an email to Reuters Health.

The findings were “surprising,” she admitted, “given that, to date, nifedipine had been shown to be a promising tocolytic for managing preterm labour. Studies in this area had demonstrated its greater effectiveness, positive impact on perinatal outcomes and reduced adverse effects when compared with betamimetics,” she explained.

There was also the added benefit that it would, potentially, be more acceptable to women given its oral route of administration and reduced adverse effects. “So, we were surprised to find that, not only was there no evidence to support the use of nifedipine for tocolysis to facilitate external cephalic version, there was also no difference in the side effect profile with no discernible differences in adverse fetal or maternal effects between women receiving nifedipine and women receiving terbutaline (although numbers were small),” Dr. Nassar said.

Two of the trials included in the review compared nifedipine with terbutaline in women with a singleton, term breech or transverse presentation. In one trial, 86 women were randomly assigned to 20 milligrams of oral nifedipine or 50 micrograms of intravenous terbutaline; the other trial, in 90 women, compared 10 milligrams oral nifedipine with 250 micrograms subcutaneous terbutaline.

The results of these trials actually suggested lower rates of successful external cephalic version among women who received nifepidine; the pooled risk ratio was 0.67 (P = 0.016).

The third trial compared two 10-milligram doses of nifedipine (and an identical placebo) given sublingually at 30 and 15 minutes prior to the procedure in 320 women with a singleton, term breech or transverse presentation.

In this trial, there was no significant between-group difference in the success rate of external cephalic version (41.6% with nifedipine and 37.2% with placebo, P = 0.43).

Overall, this review found “no evidence to support the use of nifedipine for tocolysis to facilitate external cephalic version,” the researchers report in the December 24 online issue of BJOG.

In addition, minor side effects were slightly higher with nifedipine compared with placebo.

The clinicians note that roughly 4% of term singleton infants present in the breech position and external cephalic version is an option to increase the odds of vaginal birth in these instances.

“Based on our findings,” Dr. Nassar said, “if clinicians are using nifedipine as a tocolytic to facilitate external cephalic version then they should probably change to the use of a betamimetic. For those using a betamimetic, they should continue to do so.”

The researchers point out that their analysis has its share of limitations. Because two of the trials used terbutaline, it is unclear if the findings can be generalized to all betamimetics, they note. In addition, data on secondary trial outcomes were not amenable to pooled analysis and the nifedipine and terbutaline doses differed in the two trials.

Reference:

Effectiveness of nifedipine tocolysis to facilitate external cephalic version: a systematic review

BJOG 2010. Published online December 24, 2010.