Carbetocin Versus Syntometrine for the Third Stage of Labour Following Vaginal Delivery - A Double-blind Randomised Trial

Postpartum haemorrhage(PPH)or excessive bleeding at or after childbirth is a potentially life threatening complication and is one of the major contributors to maternal mortality and morbidity worldwide (Lewis 2001).Among the various agents that have been studied in addition to the routine oxytocin and syntometrine (which has adverse effects),oxytocin agonist (carbetocin) appears to be the most promising for this indication(Chong 2004).

Carbetocin is a licensed medication for the use of prevention of postpartum haemorrhage in Singapore and many other countries. It is a long-acting synthetic octapeptide analogue of oxytocin with agonist properties.The clinical and pharmacological properties of carbetocin are similar to those of naturally occurring oxytocin. Like oxytocin, carbetocin binds to oxytocin receptors present on the smooth musculature of the uterus, resulting in rhythmic contractions of the uterus, increased frequency of existing contractions, and increased uterine tone. In pharmacokinetic studies, intravenous injections of carbetocin produced tetanic uterine contractions within two minutes, lasting six minutes, followed by rhythmic contractions for a further hour.Intramuscular injection produced tetanic contractions in less than two minutes, lasting about 11 minutes, and followed by rhythmic contractions for an additional two hours. The prolonged duration of activity after intramuscular compared with the intravenous carbetocin was significant(Hunter 1992). In comparison to oxytocin, carbetocin induces a prolonged uterine response when administered postpartum, in terms of both amplitude and frequency of contractions.

The potential advantage of intramuscular carbetocin over intramuscular oxytocin is its longer duration of action. Its relative lack of gastrointestinal and cardiovascular side-effects should also prove advantageous compared to syntometrine and other ergot alkaloids.