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Objective: To investigate the compatibility of oxytocin and tranexamic acid injection products when mixed for the purpose of co-administration by intravenous infusion. Population or Sample: Oxytocin and tranexamic acid were collected from hospitals taking part in a multicentre postpartum haemorrhage treatment (E-MOTIVE) trial in Kenya, Nigeria, Tanzania, and South Africa. Methods: The compatibility of two sentinel products of oxytocin injection and tranexamic acid injection in 200mL infusion bags of both 0.9%w/v saline and Ringer’s Lactate was assessed. We analysed all tranexamic acid -oxytocin combinations, and each evaluation was conducted for up to 6hrs. Subsequently, the compatibility of multiple tranexamic acid products with reference oxytocins products when mixed in 0.9%w/v saline over a period of 1 hour was investigated. Results: We found a significant interaction between certain oxytocin and tranexamic acid products after mixing them in vitro and observing for 1 hour. The interaction substantially impacted oxytocin content leading to reduction in concentration (14.8% - 29.0%) immediately on mixing (t=0 minutes). In some combinations, the concentration continued to decline throughout the stability assessment period. Oxytocin loss was observed in 7 out of 22 (32%) combinations tested. Conclusions: In a clinical setting, mixing oxytocin and tranexamic acid may result in an underdosing of oxytocin, compromising care in an emergency life-threatening situation. The mixing of oxytocin and tranexamic acid injection products for co-administration with IV infusion fluids should be avoided until the exact nature of the interaction and its implications are understood.