What Is Barusiban? Definition and What Research Reports

Definition

Barusiban is a synthetic peptide described in the scientific literature as a selective oxytocin receptor antagonist — a molecule that occupies the oxytocin receptor and blocks the signalling that oxytocin would otherwise trigger, without activating the receptor itself. It was studied primarily in reproductive pharmacology as an investigational tocolytic candidate, meaning a compound intended to suppress uterine contractions in the setting of preterm labour. Across the published record it appears alongside atosiban, an earlier oxytocin/vasopressin receptor antagonist, and is generally characterised in those papers as the more selective and longer-acting of the two. Barusiban is a research and investigational compound; it is not a marketed medicine, and this entry is definitional only.

What Kind of Molecule Is Barusiban?

Barusiban belongs to the family of oxytocin analogues: small, structurally constrained peptides modelled on the nine-amino-acid hormone oxytocin. Rather than reproducing oxytocin's activity, the analogue's modifications convert it into an antagonist at the oxytocin receptor, a G protein-coupled receptor expressed in myometrial (uterine smooth muscle) tissue. A receptor-mapping study compared the binding domains of the oxytocin receptor used by barusiban with those used by the agonists oxytocin and carbetocin, and reported that the antagonist and the agonists did not interact identically with the receptor (PMID 15740719). That kind of work is what places barusiban in the "selective oxytocin receptor antagonist" class rather than the broader mixed oxytocin/vasopressin antagonist class.

Because it is a peptide, barusiban is administered parenterally in the studies that describe it, and, like other peptides, its behaviour is characterised through pharmacokinetic measurements rather than assumptions carried over from small-molecule drugs. The comparative monkey study that examined its pharmacokinetic and pharmacodynamic profile alongside atosiban described barusiban as highly potent and long-acting in that model (PMID 15671092).

How the Term Is Used in Peptide Research

In peptide literature, "barusiban" is used in three fairly distinct ways:

• As a pharmacological tool. Because it is selective for the oxytocin receptor, barusiban has been used to probe which effects in a tissue or model depend on oxytocin receptor signalling specifically, as in the receptor binding-domain comparison against oxytocin and carbetocin (PMID 15740719).
• As a tocolytic candidate. The majority of published barusiban work sits in obstetric pharmacology, where the question under study was whether blocking oxytocin receptors could suppress preterm uterine activity, including in a randomised, double-blind, placebo-controlled trial in threatened preterm labour at late gestational age (PMID 19306963).
• As a comparator for atosiban. Several papers frame barusiban explicitly against atosiban, either in isolated human myometrium (PMID 15350251) or in a cynomolgus monkey model of preterm labour (PMID 15671092).

What the Published Literature Reports

Receptor-level and isolated tissue work

An in vitro study tested barusiban and atosiban against oxytocin-induced contractions of myometrium taken from preterm and term pregnant women, and reported an inhibitory effect of both compounds on those contractions (PMID 15350251). Work on the receptor itself mapped the binding domains of the oxytocin receptor engaged by barusiban in comparison to the agonists oxytocin and carbetocin (PMID 15740719). Together these two lines of evidence are what the literature draws on when it calls barusiban "selective" — the selectivity claim comes from receptor and tissue pharmacology, not from clinical outcomes.

Nonhuman primate models

Barusiban was characterised in a cynomolgus monkey model of preterm labour, where researchers compared its pharmacokinetics and pharmacodynamics with those of atosiban and described barusiban as a new highly potent and long-acting oxytocin antagonist (PMID 15671092). A subsequent report described barusiban as an effective long-term treatment of oxytocin-induced preterm labour in nonhuman primates (PMID 16914691), and a further paper reported that barusiban suppressed oxytocin-induced preterm labour in non-human primates (PMID 17570159). Separately, barusiban was used in a novel study design developed for evaluating tocolytic agents in pregnant and neonatal monkeys that incorporated behavioural and immunological endpoints (PMID 17337159).

Placental transfer

Because a tocolytic is given during pregnancy, the extent to which it crosses the placenta is a distinct research question. A 2020 study examined the placental transfer of barusiban in rabbit, monkey and human models (PMID 32307542). This is one of the later entries in the barusiban record and illustrates that preclinical characterisation of the compound continued after the clinical programme.

Clinical study

The principal human clinical entry in the published record is a randomised, double-blind, placebo-controlled trial that assessed the effect of barusiban, described there as a selective oxytocin antagonist, in threatened preterm labour at late gestational age (PMID 19306963). Readers interested in the magnitude and direction of the trial's findings should consult that publication directly rather than relying on a glossary summary.

Barusiban in the Literature at a Glance

Tolerability and Safety Endpoints: What Studies Report

Safety-relevant endpoints in the barusiban record were addressed mainly through preclinical design rather than through a large clinical safety database. One nonhuman primate programme was explicitly constructed to evaluate tocolytic agents in pregnant and neonatal monkeys using behavioural and immunological endpoints, with barusiban as the test compound (PMID 17337159). Placental transfer was studied separately across rabbit, monkey and human models (PMID 32307542), and human tolerability was assessed within the randomised, double-blind, placebo-controlled trial in threatened preterm labour at late gestational age (PMID 19306963). No adverse-event rates are reproduced here; the primary publications are the appropriate source for those details.

What the Literature Does Not Establish

The published barusiban record is narrow and obstetric. It does not describe use outside pregnancy-related oxytocin receptor pharmacology, and the sources listed here contain no findings on body composition, athletic performance, cognition, or any consumer-facing application. Barusiban is not an approved medicine and is encountered chiefly as an investigational and research compound; where peptides are supplied for laboratory work they are typically labelled research-use-only and are not intended for human administration. Terminology matters too: barusiban is an antagonist, the functional opposite of oxytocin agonists such as carbetocin, which was used as a comparator in the receptor-mapping study (PMID 15740719).

This page is for educational purposes only and is not medical advice; consult a licensed physician about any medical question or decision. It summarises what the cited studies reported and does not describe how any compound should be used.

References

• Barusiban, a selective oxytocin receptor antagonist: placental transfer in rabbit, monkey, and human (Biology of Reproduction, 2020)
• Barusiban, a new highly potent and long-acting oxytocin antagonist: pharmacokinetic and pharmacodynamic comparison with atosiban in a cynomolgus monkey model of preterm labor (The Journal of Clinical Endocrinology and Metabolism, 2005)
• Inhibitory effect of barusiban and atosiban on oxytocin-induced contractions of myometrium from preterm and term pregnant women (Journal of the Society for Gynecologic Investigation, 2004)
• Binding domains of the oxytocin receptor for the selective oxytocin receptor antagonist barusiban in comparison to the agonists oxytocin and carbetocin (European Journal of Pharmacology, 2005)
• Barusiban, an effective long-term treatment of oxytocin-induced preterm labor in nonhuman primates (Biology of Reproduction, 2006)
• The effect of barusiban, a selective oxytocin antagonist, in threatened preterm labor at late gestational age: a randomized, double-blind, placebo-controlled trial (American Journal of Obstetrics and Gynecology, 2009)
• Use of barusiban in a novel study design for evaluation of tocolytic agents in pregnant and neonatal monkeys, including behavioural and immunological endpoints (Reproductive Toxicology, 2007)
• Barusiban suppresses oxytocin-induced preterm labour in non-human primates (BMC Pregnancy and Childbirth, 2007)