(5) Comparison of Meal-Time Dosing of Rapid Acting Insulin Using Carbohydrate Counting vs. Fixed Doses Utilizing Continuous Glucose Monitoring in Patients with Cystic Fibrosis Related Diabetes

Background: Optimizing prandial bolus insulin dosing is essential for cystic fibrosis-related diabetes (CFRD) management but is challenged by the traditionally high-calorie diet prescribed to maintain ideal BMI and the demands of close glucose monitoring. This study leveraged glucose monitoring (CGM) to compare fixed meal dosing vs carbohydrate count-based insulin dosing.

Methods: Patients with CFRD treated with meal-time rapid-acting insulin were recruited. Carbohydrate counting education was provided by a dietician and the insulin carbohydrate ratio was determined by the total daily insulin dose at the study start. Abbott Freestyle Flash Libre CGMs were worn for 14-days. For the first 7 days, participants used fixed mealtime insulin dosing (fixed dosing week, FDW), and for the second 7 days used carbohydrate-counting based insulin dosing (carbohydrate count week, CCW) using the ‘rule of 500’ to calculate insulin to carbohydrate ratio. We also compared the frequency and duration of hypo- and hyperglycemia between the two insulin delivery methods.

Results: Six (3F/3M; aged 65 +/- 7.7 years; 2 F508del homozygous, 2 F508del heterozygous, 2 with unknown mutation status) of the recruited 9 participants had complete data (3 dropped out or had CGM malfunction). All subjects were on triple modulator therapy for at least 12 months. Average CFRD duration was 8.6 +/-2.9 years, A1c was 7.3 +/- 0.5%, and weight was 55 +/-5.4 kg. ICR ranged from 1:10 grams to 1:17 grams Average sensor glucose was not different in FDW 7.27+/- 0.83 mmol/l vs. CCW 7.04+/- 0.88 mmol/l (p=0.8). No differences in TIR [CCW (984 minutes +/- 86) vs. FDW (919 +/-110 minutes); p=0.6], or number of low glucose events [FDW: 11 vs. CCW: 9 events; p=0.6].

Conclusions: Limited studies have examined the efficacy of carbohydrate counting to dose mealtime insulin vs fixed pre-meal insulin doses. Future larger studies that use CGM to optimize insulin to carbohydrate-based dosing are needed to determine the glycemic benefit of this approach vs the additional patient burden of carbohydrate counting.

Acknowledgements: This work was supported by the Cystic Fibrosis Foundation through the 'EnVision CF: Emerging Leaders in CF Endocrinology II Program' and by the University of Pittsburgh Adult Cystic Fibrosis Program and Dr. Joseph Pilewski

References: