How many Lantus (insulin glargine) pen injectors are needed for a patient who uses 20 units daily for one month?

Lantus Pen Supply Calculation for 20 Units Daily

A patient using 20 units of Lantus daily will need 2 insulin pens per month. 1

Mathematical Calculation

• Standard Lantus SoloStar prefilled pens contain 300 units of insulin (3 mL of U-100 insulin) 1, 2
• At 20 units per day, one pen lasts: 300 units ÷ 20 units/day = 15 days 1
• Monthly requirement: 30 days ÷ 15 days per pen = 2 pens 1

Practical Considerations That May Affect Supply

• Priming and wastage: Each pen requires priming before injection, which uses small amounts of insulin and may leave residual insulin after the final dose 3
• Premature needle withdrawal: Laboratory studies demonstrate that premature needle withdrawal can result in 2.6-8.6% insulin underdelivery per injection, potentially requiring dose adjustments 4
• Proper injection technique: Maintaining the needle in place for the full duration after injection is critical to ensure complete dose delivery 4

Prescription Recommendation

• Prescribe 2 pens per 30-day supply for a patient using exactly 20 units daily 1
• Consider prescribing 3 pens per month if the patient has technique issues, requires dose adjustments, or needs a buffer for wastage 3
• Insurance coverage typically provides 30-day supplies, which would be 2 pens for this dosing regimen 3

Device Specifications

• Lantus SoloStar is a disposable prefilled pen that is discarded after all 300 units are used 2
• The pen allows dose selection from 1 to 80 units in 1-unit increments 2
• Each pen can be used for multiple injections until the 300-unit capacity is exhausted 2

Storage and Handling

• Unopened pens should be refrigerated at 2°C–30°C (36°F–86°F) 5
• In-use pens can be kept at room temperature to reduce injection-site discomfort 5
• Remove the pen from refrigeration at least 1 hour before injection, as cold insulin is more painful to inject 2