GSK announced the start of a phase III programme to evaluate the efficacy and safety of retosiban, an investigational oxytocin antagonist. Retosiban is being developed as a potential treatment to improve neonatal outcomes of babies born to women in spontaneous preterm labour by prolonging the time to delivery.

A preterm (or premature) birth is when a baby is born at least three weeks before the expected due date. The earlier a baby is born, the more severe the baby’s health problems are likely to be. Some preterm babies require special care to stay alive and can spend months in hospital in a neonatal intensive care unit and some may suffer lifelong consequences.

The first study in the retosiban phase III programme is designed to demonstrate the efficacy and safety of retosiban in women with spontaneous preterm labour when compared with atosiban, an oxytocin/vasopressin antagonist. The primary outcome measure of this study is the time to delivery after the start of treatment. The key secondary endpoints will measure neonatal morbidities and mortality. A follow-up study will assess the long-term safety and outcomes of the infants born to mothers participating in the retosiban treatment studies. Further studies are also planned.

Pauline Williams, vice president and head of GSK Maternal & Neonatal Health Unit said: “Preterm birth is a leading cause of illness and death in newborns and infants worldwide. As part of our efforts to address this issue, we are evaluating whether retosiban can potentially stop preterm labour and whether increasing the gestational age of a newborn baby can reduce the complications of prematurity.”

Retosibanis not approved or licensed for use anywhere in the world.

Preterm labour is when an expectant mother experiences uterine contractions and cervical changes before the 37th week of pregnancy.  Full term birth is considered to be 40 weeks gestational age. Spontaneous preterm labour accounts for approximately 40-50% of preterm births and is the leading cause of worldwide morbidity and death in newborns and infants; mortality and morbidity are inversely proportional to gestational age. An estimated 15 million babies are born preterm every year worldwide.

Pre-clinical data has shown that retosiban is a potent and highly selective oxytocin receptor antagonist. The clinical relevance of these data is unknown. Retosiban is thought to work by blocking the effects of oxytocin, a hormone produced by the body during labour, in order to stop preterm labour and thereby increase gestational age at birth.