Introduction: Gestational Diabetes Mellitus (GDM) management continues to evolve; however few studies have evaluated drug utilisation to improve sustainability. We aimed to determine the total requirement of women commenced on isophane insulin, to reduce resource wastage in the GDM setting.
Method: We conducted a retrospective antenatal audit of women diagnosed with GDM at Mater Mothers’ Hospital, Brisbane between 1/01/2018 and 01/10/2020 and prescribed isophane insulin (Protophane®). Mater Mothers’ Hospital is a large quaternary centre servicing a culturally diverse community. Antenatal records were reviewed to determine their actual insulin usage. Those diagnosed prior to week 24 were grouped separately to reduce confounding. Primary outcome was the average insulin requirement at term compared with insulin supplied.
Results: For 1,981 identified women, 604 met the inclusion criteria. Of this group, 86 women were excluded due to incomplete records: interhospital transfer or moving interstate. The remaining 518 women were stratified, with the 386 diagnosed at/post-week 24 having a mean insulin requirement at term of 26iu daily (median 22iu) versus 132 women pre- week 24 with a mean final insulin requirement at term of 40iu daily (median 34iu). An isophane insulin requirement of 45iu was found to service the needs of 88% of the GDM population requiring isophane insulin. The outpatient supply of insulin was largely serviced by community providers with only 16% having their prescription filled onsite.
Conclusion: Our results strongly indicate that the current practice of supplying 5x5 pens of isophane insulin (current PBS maximum supply) is a gross patient oversupply. Supplying patients with 3x5 pens would meet the majority of insulin needs and greatly reduce the cost burden to the PBS, with an estimated national savings of $812,736 based on Australian Bureau of Statistics data. We plan to pilot a programme of staged dispensing to address this issue, reducing the pharmaceutical footprint of GDM management.