Insulin Pen Requirements for a 90-Day Supply at 20 Units Daily
For a patient requiring 20 units of insulin daily for 90 days, 9 standard insulin pens would be needed. 1
Calculation of Required Insulin Pens
- Standard insulin pens contain 300 units of insulin (3 mL of U-100 insulin) 1, 2
- At 20 units per day, one pen would last: 300 units ÷ 20 units/day = 15 days 1
- For a 90-day supply: 90 days ÷ 15 days per pen = 6 pens (minimum) 1, 2
- However, additional pens should be prescribed to account for:
Practical Considerations
- Most commercially available insulin pens contain air bubbles at purchase (average estimated to be 50 microliters), which can reduce insulin delivery 4
- With significant air in the cartridge (200 microliters), a patient might receive only 37% of the expected dose if the needle is withdrawn after the recommended 5 seconds 4
- To ensure adequate supply and account for these factors, prescribing 9 pens for a 90-day supply is recommended 1, 2
Administration Recommendations
- Insulin should be injected into subcutaneous tissue of the abdomen, thigh, buttock, or upper arm 5
- The abdomen has the fastest absorption rate, followed by arms, thighs, and buttocks 5
- Rotation of injection sites is important to prevent lipohypertrophy or lipoatrophy 5
- 4-mm pen needles inserted at 90° are recommended for all adults regardless of age, sex, ethnicity, or BMI 5
Important Safety Considerations
- Needles should be removed immediately after each injection to prevent air accumulation in insulin cartridges 3, 4
- Patients should be advised not to share insulin pens to avoid possible transmission of disease 3
- Proper disposal of needles in puncture-resistant containers is essential 3
Advantages of Insulin Pens
- Insulin pens are designed to provide a convenient and easy means of insulin administration 6
- They are often less painful than the vial-and-syringe method 6
- Pens are associated with greater patient preference and social acceptability, which may help improve glycemic control 6
By prescribing 9 insulin pens for a 90-day supply at 20 units daily, you ensure the patient has adequate insulin while accounting for practical considerations in insulin pen use.