The central role of calcium in the biochemistry of myome-trial contractions led to the exploration of the use of calcium channel blockers, specifically nifedipine, as a tocolytic drug. Because there has been no interest from the pharmaceutical industry in promoting nifedipine for this indication, there have only been small, locally funded comparison trials of nifedipine versus sympathomimetics. There are no placebo-controlled trials of nifedipine as a tocolytic. Meta-analysis of the sympathomimetic comparison trials suggest that nifedipine may be superior in its ability to delay delivery and is associated with a reduction in the rate of respiratory distress syndrome and intraven-tricular haemorrhage in preterm neonates, although not with any improvement in perinatal mortality. It is unlikely that there will ever be any large-scale placebo-controlled trials of nifedipineor any largetrials comparing nifedipine with atosiban. There has been one study which indirectly compared atosiban with nifedipine by taking advantage of the fact that each had been compared with sympa-thomimetic drugs. This study suggested that nifedipine is superior to atosiban in delaying delivery and, unlike
Undelivered at 48 hours
Risk of RDS
Fig. 21.5 Indirect comparison for Atbosiban with Nifedipine in the acute management of preterm labour. Adapted from Coomarasamy A et al. BJOG. 2003 110(12): 1045-9.
atosiban, is associated with a reduction in the risk of respiratory distress syndrome (Fig. 21.5).
At the present time the obstetrician has a choice between atosiban and nifedipine and it is probably reasonable, in our current state of knowledge, not to use tocolytic therapy at all. More specific oxytocin antagonists are in development, as are drugs which target other receptors, such as prostaglandin receptors. It is probable that the disappointing results of tocolytics in trials to date may be because of poor trial design and, in particular, the high placebo response rates. In future trials which are able to target tocolytic drugs more specifically at women genuinely in preterm labour, for example, by taking advantage of fetal fibronectin testing, may more properly define the potential value of tocolytic therapy.
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Once your pregnancy is over and done with, your baby is happily in your arms, and youre headed back home from the hospital, youll begin to realize that things have only just begun. Over the next few days, weeks, and months, youre going to increasingly notice that your entire life has changed in more ways than you could ever imagine.