Insulin Pen DOS Reference

🖊️ Multi-Dose Insulin Pens

Calculation Steps

Calculate Total Units per Day: (Prescribed units per dose + Priming units) × Doses per day = Total units/day
Calculate Days per Pen: Units per pen ÷ Total units/day = Days per pen
Calculate Pens to Dispense: Days prescribed ÷ Days per pen = Number of pens
Calculate DOS: (Pens dispensed × Units per pen) ÷ Total units/day = DOS

Critical: Insulin pens require priming before each injection. Standard priming is 2 units per dose. This waste must be included in DOS calculations.

Example: Novolog FlexPen (15 mL box = 5 pens × 3 mL = 1500 units)
Inject 20 units subcutaneously three times daily with meals

Step 1 — Total units/day: (20 units + 2 priming) × 3 = 66 units/day
Step 2 — Days per pen: 300 units/pen ÷ 66 units/day = 4.5 days/pen
Step 3 — DOS for 1 box: 4.5 days/pen × 5 pens = 22.5 → 22 DOS

In-Use Guidelines: Follow manufacturer guidelines (typically 28 days max after opening). If calculated DOS exceeds in-use limit, annotate prescription and add "discard after X days" to directions.

🎓 Supplemental Training — Insulin Pens

Step 1 of 3

Step 1: Find total units per day

Novolog FlexPen — 20 units TID with 2 priming units per dose.

(20 + 2 priming) × 3 doses = 66 units/day

Add priming units to each dose, then multiply by daily dose frequency.

Step 2: Find days per pen

Each Novolog FlexPen contains 300 units.

300 units ÷ 66 units/day = 4.5 days/pen

Divide total pen units by daily usage. Always round DOWN — so 4.5 → 4 days per pen.

Step 3: Find DOS for 1 box (5 pens)

4.5 × 5 pens = 22.5 → 22 DOS

Multiply days per pen by number of pens. Round down the final result.

Full Worked Example — Novolog FlexPen

Rx: Novolog FlexPen 3mL × 5 (1 box = 1500 units total)

Directions: Inject 20 units subcutaneously three times daily with meals

Units/day = (20 + 2) × 3 = 66 units/day Days/pen = 300 ÷ 66 = 4.5 days DOS = 4.5 × 5 pens = 22.5 → 22 DOS

⚠️ 22 DOS is within the 28-day in-use cap — no annotation needed.

Step 1 of 3

Step 1: Find total units per day

Lantus SoloStar — 30 units QHS (once nightly) with 2 priming units.

(30 + 2) × 1 dose = 32 units/day

QHS = once daily (at bedtime). Add 2 priming units and multiply by 1 dose per day.

Step 2: Find days per pen

Lantus SoloStar holds 300 units.

300 ÷ 32 = 9.37 days/pen

300 units per pen divided by 32 units consumed daily = 9.37 days of use per pen.

Step 3: Apply in-use cap

9.37 × 5 pens = 46.8 → 46 days BUT 28-day in-use cap applies
Final DOS = 28

The calculated DOS (46 days) exceeds the 28-day in-use limit for opened insulin pens. The final billed DOS must be capped at 28 days.

Full Worked Example — Lantus SoloStar

Rx: Lantus SoloStar 3mL × 5 (1 box = 1500 units total)

Directions: Inject 30 units subcutaneously once nightly

Units/day = (30 + 2) × 1 = 32 units/day Days/pen = 300 ÷ 32 = 9.37 days Raw DOS = 9.37 × 5 = 46.8 → 46 days In-use cap applied → Final DOS = 28

⚠️ Annotate prescription: "Discard after 28 days of opening."

Step 1 of 4

Step 1: Determine units per pen

Toujeo SoloStar is a U-300 pen.

1.5 mL × 300 units/mL = 450 units/pen

Toujeo is U-300 (300 units/mL) in a 1.5 mL pen — higher concentration than standard U-100 pens. Always verify units/pen from the product labeling.

Step 2: Find total units per day

40 units QHS with 2 priming units.

(40 + 2) × 1 dose = 42 units/day

Add 2 priming units to each prescribed dose, then multiply by daily frequency.

Step 3: Find days per pen

450 ÷ 42 = 10.7 → 10 days/pen

450 units per pen ÷ 42 units/day = 10.7. Always round DOWN to 10 days per pen.

Step 4: Apply in-use cap

10 days/pen × 3 pens = 30 DOS → 28-day cap applies
Final DOS = 28

Calculated DOS of 30 days exceeds the 28-day in-use cap. Final billed DOS is capped at 28 days.

Full Worked Example — Toujeo SoloStar

Rx: Toujeo SoloStar U-300 1.5mL × 3 pens

Directions: Inject 40 units subcutaneously once nightly

Units/pen = 1.5 mL × 300 units/mL = 450 units/pen Units/day = (40 + 2) × 1 = 42 units/day Days/pen = 450 ÷ 42 = 10.7 → 10 days/pen Raw DOS = 10 × 3 pens = 30 days In-use cap applied → Final DOS = 28

⚠️ Annotate prescription: "Discard after 28 days of opening."

📊 DOS Formula — Animated Infographic

Total Pens
Prescribed ÷ Units Used
Per Day = Raw DOS → Final DOS

Hover over each chip for details. Click Animate to highlight calculated values.

📹 Video Coming Soon — Insulin Pen DOS Walkthrough

🧮 Live DOS Calculator — Insulin Pens

Prescribed units per dose

Doses per day (frequency)

Units per pen

Number of pens dispensed

Priming units per dose (default: 2)

In-use cap in days (default: 28)

① Units used per day (with priming)

(Units/dose + priming) × doses/day = total units consumed daily

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② Total units from pens prescribed

Units per pen × number of pens dispensed (Total Pens Prescribed × units/pen)

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③ Raw DOS (calculated)

Total units from pens prescribed ÷ units used per day, rounded down

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④ Final DOS (after in-use cap)

min(Raw DOS, in-use cap). The in-use cap limits how long an opened insulin pen can be used.

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Days of Supply

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Enter values above to calculate

⚠️ In-use cap is limiting — the cap is shorter than the calculated DOS.

🖊️ Insulin Pen DOS Reference

Calculation Steps

Step 1: Find total units per day

Step 2: Find days per pen

Step 3: Find DOS for 1 box (5 pens)

Full Worked Example — Novolog FlexPen

Step 1: Find total units per day

Step 2: Find days per pen

Step 3: Apply in-use cap

Full Worked Example — Lantus SoloStar

Step 1: Determine units per pen

Step 2: Find total units per day

Step 3: Find days per pen

Step 4: Apply in-use cap

Full Worked Example — Toujeo SoloStar

📊 DOS Formula — Animated Infographic

🧮 Live DOS Calculator — Insulin Pens