Pharmacokinetics and Safety of Inhaled Oxytocin Compared with Intramuscular Oxytocin: The First Randomised Open-Label Study in Women in the Third Stage of Labour

Abstract

Background: Intramuscular (IM) oxytocin for postpartum haemorrhage (PPH) prevention in resource-poor settings is limited by the need for cold-chain storage and skilled staff for safe injection. We compared the pharmacokinetics (PK) and safety of heat-stable oxytocin inhaled (IH) versus IM administration in women during third stage of labour (TSL). Methods: The phase 1, randomised, open-label clinical study (NCT02999100) was conducted across three centres in the UK and Australia. Participants (Group 1, women in TSL; Group 2, non-pregnant women of childbearing potential) were randomised 1:1 via validated GSK internal software: Group 1, oxytocin 240 IU (400 μg) IH or oxytocin 10 IU (17 μg) IM immediately after delivery; Group 2, intravenous (IV) oxytocin 5 IU (8·5 μg) and oxytocin 240 IU (400 μg) IH at two separate dosing sessions in a cross-over design. Primary endpoints included characterising oxytocin IH PK. The safety population included patients who received ≥1 dose; any PK sample obtained and analysed was included in the PK population. Additional investigations explored the validity of the PK concentration data. Findings: Participants were recruited between November 2016 and March 2019. In Group 1, 29 participants were randomised; 17 received IH (n=9) or IM (n=8) oxytocin. After IH and IM administration most plasma oxytocin concentrations were below quantification limits (2 pg/ml). In Group 2 (n=14), oxytocin IH concentrations remained quantifiable up to 3 hrs post dose. Adverse events were reported for: Group 1, IH n=3 (33%) and IM n=2 (25%); Group 2, n=14 (100%). No deaths were reported. Interpretation: Safety profiles of oxytocin IH and IM were similar; PK profiles could not be defined for oxytocin IH or IM in women in TSL, despite using a highly sensitive assay. Ex vivo investigations suggested oxytocin metabolism occurred in vivo and not during sample collection and processing. Trial Registration: Trial Registration Number, (ClinicalTrials.gov: NCT02999100). The study protocol can be found online (https://clinicaltrials.gov/ProvidedDocs/00/NCT02999100/Prot_000.pdf). Funding: GlaxoSmithKline (GSK 205920; NCT02999100) Declaration of Interest: KG-K, AS-C, KRP, PL, TN, JM, CG, CK and VLO have no conflicts to declare. SK, AC, RAG, SP, IS, AS, KH, MP, ME and SS are employees of and hold stocks in GSK. MPM is an inventor on the patent method and formulation for oxytocin inhalation (WO2013/016754 A1 [PCT/AU2011001430]). Ethical Approval: The study protocol was reviewed and approved by the Office for Research Ethics Committees of Northern Ireland (UK) and the Monash Health Human Research Ethics Committee (Australia) in accordance with Good Clinical Practice (GCP) guidelines.