Background Intravenous unfractionated heparin (IVUFH) and low molecular weight heparins (LMWH) are first line anticoagulants for the management of acutely unwell patients. The decision to prescribe either IVUFH or an LMWH is complex with minimal direction from clinical guidelines. The aim of this study was to explore individual prescribers’ perceptions on prescribing IVUFH or LMWH in patients’ acute management.

Methods Semi-structured interviews were conducted with purposively selected senior medical officers who were from specialities including cardiology, cardiothoracic surgery, respiratory, emergency, vascular surgery, nephrology, neurology and general medicine, identified as those that routinely prescribe IVUFH or LMWH. An interview tool with seven questions and four hypothetical case scenarios guided interview discussions. Interviews were audio recorded, transcribed and inductively coded for thematic analysis.

Results Twelve doctors participated in interviews between February and October 2022. Mean interview duration was 24 min; data saturation was achieved. Most were senior doctors: one was a registrar and others were staff specialists. Three key themes emerged: (1) rationale for the choice of heparinoid, (2) patient safety considerations and (3) resources required. The themes and subthemes identified the complexity of issues to consider when choosing between IVUFH and LMWH. Multiple factors were considered by participants which were based on previous experiences and institutional capabilities rather than evidence-based medicine.

Conclusion Future interventions should focus on highlighting LMWH as the preferred heparinoid in most clinical scenarios. The use of IVUFH should be reserved for specific patient cohorts where the benefit of IVUFH outweighs the additional risks.