Prescription Requirements for Insulin Pump Therapy
You do not need to include a maximum daily dose on a prescription for rapid-acting insulin used in an insulin pump. Insulin pumps are designed to deliver individualized, variable doses throughout the day based on the patient's programmed basal rates, carbohydrate intake, and correction needs—making a fixed maximum dose both impractical and potentially unsafe.
Why a Maximum Daily Dose Is Not Required
Insulin pumps deliver highly individualized dosing that varies continuously based on programmed basal rates (which can change hourly), meal-time boluses calculated from carbohydrate-to-insulin ratios, and correction doses determined by insulin sensitivity factors—none of which can be captured by a single maximum dose 1.
Total daily insulin requirements vary significantly even within the same patient: in type 1 diabetes, typical ranges are 0.4–1.0 units/kg/day, but can exceed 1.5 units/kg/day during puberty, pregnancy, or acute illness 2, 3.
Basal insulin in pump therapy accounts for approximately 30–50% of total daily dose (not the traditional 50%), with the remainder delivered as meal-time and correction boluses 4, 3. This distribution shifts dynamically based on activity, illness, and dietary intake 1.
Pump users require the flexibility to adjust doses in real-time using on-board calculators that account for active insulin, carbohydrate intake, and current glucose levels—a maximum dose would create dangerous barriers to appropriate dose escalation 1, 5.
What Should Be on the Prescription
Instead of a maximum dose, the prescription should specify:
- Insulin type: Rapid-acting analog (e.g., NovoRapid®, Humalog®, Apidra®) 1
- Delivery method: Continuous subcutaneous insulin infusion (insulin pump)
- Quantity: Sufficient supply for the prescribed duration (e.g., "insulin cartridges/vials as needed for pump therapy")
- Refill instructions: Typically monthly refills based on estimated usage
Clinical Rationale
Pump therapy mimics physiological insulin delivery with continuous basal infusion and on-demand boluses, requiring instantaneous dose changes that cannot be predetermined 1.
Carbohydrate-to-insulin ratios vary throughout the day: breakfast typically requires more insulin per gram of carbohydrate (CIR ≈ 1:10 using the formula 300÷TDD) compared to lunch and dinner (CIR ≈ 1:13–15 using 400÷TDD) due to counter-regulatory hormones 3, 1.
Insulin sensitivity factors (correction factors) are calculated as 1500÷TDD and must be adjusted based on individual response, making fixed maximum doses inappropriate 1, 4.
Duration of insulin action in pumps is approximately 3–5 hours for rapid-acting analogs, but pump calculators account for "insulin on board" to prevent dose stacking—a process that requires flexible dosing 5, 1.
Safety Considerations
Patients on pump therapy should be capable of using the device safely (either independently or with caregiver assistance) and have received comprehensive education on pump management 6.
Glycemic status should be assessed at least every 3 months with HbA1c monitoring to ensure appropriate overall insulin dosing 6.
Pump users require self-management skills including carbohydrate counting, correction dose calculation, and recognition of pump malfunction or infusion site problems 1, 7.
Common Pitfalls to Avoid
Do not prescribe a maximum daily dose as this creates artificial barriers to appropriate dose escalation during illness, growth spurts, or changes in activity level 2, 4.
Do not use traditional 50:50 basal-to-bolus ratios when programming pumps; recent evidence shows basal requirements are closer to 30–40% of total daily dose in well-controlled patients 4, 3.
Avoid using the outdated "500 rule" for carbohydrate ratios; the formulas 300÷TDD (breakfast) and 400÷TDD (lunch/dinner) more accurately reflect actual insulin requirements 3, 4.
Never assume pump therapy is appropriate for all patients; those unable to perform self-monitoring, carbohydrate counting, or pump troubleshooting should use multiple daily injections instead 6, 7.