Introduction British Columbia Emergency Health Service trialled the use of intranasal (IN) ketamine given by Primary Care Paramedics (PCPs). Prior to this practice change, the PCPs had not performed weight-based drug calculations, given medications intranasally, nor been responsible for controlled and targeted substances. This study aimed to use the Capability, Opportunity, Motivation and Behaviour (COM-B) model and Theoretical Domain Framework (TDF) to identify enablers and barriers to implementing IN paramedic administered ketamine analgesia (iPAKA) for PCPs. Methods This was a parallel convergent mixed methods study with two phases. The quantitative phase consisted of longitudinal staff surveys to assess PCP knowledge and perceptions of ketamine and controlled and targeted substances policies. The qualitative phase involved staff focus groups on programme implementation. Descriptive statistics of survey results were integrated with coded focus group data and analysed using the COM-B model and TDF. Evidence-based behavioural change techniques were mapped to each TDF domain. Findings Our analysis revealed barriers and enablers across several TDF domains. Implementing ketamine was enabled by quality education, strong organisational support and the availability of cognitive aides. Trial success was attributed in part to participant's feelings of optimism and their increased job satisfaction. Key barriers included a knowledge gap involving drug dosage calculations, negative emotions associated with performance anxiety and a lack of field education and supervision to monitor paramedic practice. Conclusion The use of theoretical frameworks and models like COM-B/TDF serves to improve the sustainable implementation of behaviour and clinical practice change in paramedicine. When project teams use theory to guide design and implementation, they can systematically identify and target individual and organisational enablers and barriers to adopting routine practices. The iPAKA study reveals key barriers and facilitators in several TDF domains and presents theory-linked targeted behavioural techniques to support on-going implementation of PCP-administered IN ketamine for analgesia.