Atosiban (Tractocile), an oxytocin antagonist for delaying premature birth, has been launched this week (see p892).
Atosiban acts by preventing oxytocin from binding to its receptors in the uterus. This inhibits uterine contractions. The drug has also been shown to inhibit the effects of vasopressin by binding to its receptor.
The manufacturer, Ferring, reports that phase III clinical trials showed atosiban to be superior to a beta-agonist. Beta-agonists, particularly ritodrine, are currently used to prevent premature birth. Atosiban was given to 201 women with pre-term labour at 23-33 weeks gestation and a beta-agonist to 163 women. The proportion of women who remained undelivered and not requiring alternative treatment within seven days of therapy initiation was 59.6 per cent for atosiban and 47.7 per cent for the beta-agonist. Most treatment failures were caused by poor tolerability but insufficient efficacy occurred in 14.2 per cent of the atosiban group and 5.8 per cent of the beta-agonist group.
Ferring comments that that pre-term birth occurs in 5.9 per cent of all births. At 23-26 weeks gestational age, each day gained improves infant survival by 3 per cent, the company adds.