Clinical PEARLS for prescribing insulin

We've spent the last couple of weeks building insulin regimens. This one is the practical layer: the tips, scripts, and supply details that make prescribing insulin painless and keep the pharmacy from calling you back.

1) Know your concentrations and containers

• Most insulins are U-100 (100 units/mL).
• Higher strengths (U-200 glargine/degludec, U-300 glargine, U-500 regular) are for very high daily doses, usually with endocrinology on board.
• Common package sizes:
  • Vial: 10 mL = 1,000 units (U-100)
  • Pen pack: 5 pens x 3 mL each = 1,500 units total (U-100)

2) Put this on every Rx

• "May change per insurance formulary."
• Frequency of injections and testing, or the script bounces back.
• For supplies: device name plus compatible strips, lancets, or pen needles, plus frequency.

3) Sample insulin prescriptions (copy and paste)

Vial and syringe example (basal start)

Insulin glargine (Lantus) U-100 vial, 10 mL
Sig: Inject 10 units subcutaneously nightly. May titrate per clinic instructions.
Disp: 1 vial (10 mL = 1,000 units) Refill: 2
Notes: May change per insurance formulary.

Pen example (often covered more easily)

Insulin glargine (Basaglar or Lantus) U-100, 3 mL pens (pack of 5; total 1,500 units)
Sig: Inject 10 units SC nightly. May titrate per clinic instructions.
Disp: 1 carton (5 pens) Refill: 2
Needles: 32G 4 mm pen needles, use with each injection, Disp: 100, RF: 2
Notes: May change per insurance formulary.

Rapid-acting add-on (meal dose)

Insulin aspart (Novolog or Fiasp) U-100, 3 mL pens
Sig: Inject 4 units SC 0 to 15 minutes before lunch (see titration plan).
Disp: 1 carton (5 pens) Refill: 2
Notes: May change per insurance formulary.

4) Syringes and pen needles (what to choose)

Syringes (U-100):

• 0.3 mL = up to 30 units (best if doses <30 u)
• 0.5 mL = up to 50 units
• 1.0 mL = up to 100 units

For example, a patient taking 20 u BID is a perfect fit for a 0.3 mL syringe.

Pen needles: 31 to 33G, 4 to 6 mm length works for most adults. They're less painful and many patients don't need to pinch the skin.

5) Quantity math (so you don't get callbacks)

• Daily dose x 30 = monthly units needed.
• Compare that to container totals to pick the right quantity.

A couple of worked examples:

• 40 u/day = 1,200 units/month = 2 vials (2 x 1,000 = 2,000 u) or 1 pen carton (1,500 u).
• 20 u BID (40 u/day) with pens: "Dispense 1 carton; RF 2."

6) Don't forget the testing and CGM supplies

BGM kit

Glucometer (brand per formulary)
Test strips, use to check glucose BID (AM fasting and pre-dinner), Disp: 100, RF: 2
Lancets, use BID, Disp: 100, RF: 2
Lancing device as needed
Alcohol swabs, PRN

Many plans allow BID checks by default, and some will cover QID for insulin-treated patients.

CGM options (verify coverage criteria):

• Freestyle Libre 14-day/2-week sensors; Libre 3 real-time
• Dexcom G6/G7. Include receiver/app, sensors, and transmitter (if applicable).

7) Patient instructions that prevent calls

• Hypoglycemia plan (15-15 rule): 15 g fast carbs, recheck in 15 min, repeat if <70.
• Injection timing: basal same time daily; rapid analogs 0 to 15 min before meals; regular ~30 min before.
• Site rotation: abdomen, thighs, upper arms; move 1 to 2 inches each time.
• Storage: unopened pens/vials in the fridge; open pen typically room temp per label (check the brand).
• Travel: keep a backup pen/vial and glucose tabs on hand.

8) EMR SmartPhrase (toss this in your note or message)

Insulin/Supplies Plan: U-100 insulin prescribed. Starting dose 10 u QHS (or per regimen). Supplies ordered: [pen needles or syringes], meter/strips/lancets BID testing (increase if needed), or CGM if covered. Rx includes "may change per insurance formulary." Patient instructed on injection technique, site rotation, hypoglycemia (15-15 rule), storage, and sharps disposal. Follow-up 2 to 4 weeks or sooner for BG <70 or persistent BG >300.

9) Pearls that save sanity

• Formulary swap language prevents about 90% of pharmacy callbacks.
• If the nightly basal dose creeps >50 to 60 u, consider splitting to BID for smoother coverage.
• NPH is fine (and OTC) when cost is the barrier. Teach a bedtime snack and watch for nocturnal lows.
• Many patients on GLP-1s need less prandial insulin, so titrate down to avoid lows.
• Put the quantity math in your note so future you knows why you chose that amount.

Frequently asked questions

How do I figure out how much insulin to dispense?
Daily dose times 30 gives the monthly units needed, then match that to container totals. A 10 mL U-100 vial is 1,000 units and a pen carton (5 x 3 mL) is 1,500 units. For example, 40 u/day needs 1,200 units/month, so 2 vials or 1 pen carton.

What phrase stops pharmacy callbacks?
Add "may change per insurance formulary" to every insulin Rx, and always include frequency of injections and testing plus the device name for supplies. That formulary swap language alone prevents about 90% of callbacks.

Which syringe or pen needle should I pick?
Pick the syringe by dose: 0.3 mL for up to 30 units, 0.5 mL for up to 50, 1.0 mL for up to 100. For pen needles, 31 to 33G and 4 to 6 mm works for most adults.

When should I move from a fingerstick meter to CGM?
Many plans cover CGM for insulin-treated patients, so it's worth checking coverage once a patient is on insulin. Verify the criteria, then order the receiver/app, sensors, and transmitter if applicable.

Education only, not medical advice. Use your clinical judgment, local protocols, and current guidelines.

If you're earlier in the workflow, start with starting basal insulin, then move to adding mealtime insulin once fasting is controlled. To keep the scripts, supplies, and CGM ordering on one page at the visit, the Clinical Desk Reference ($37) is the quick version, and the Primary Care Clinical Mastery Program covers the full diabetes system if you want to go deeper.

Written by Allison Sowders, MSN, APRN, FNP-BC, a practicing primary care nurse practitioner and founder of Nurse Practitioner Mentor. Reviewed July 2026.