Preferred in FITTER Forward
A short pen needle reaches the fat beneath the skin with less risk of reaching muscle. Most adults use a 90° angle; a skin lift may be needed when there is little fat beneath the skin.
TruCore field notes
Injection & medication care
Technique matters
A small needle.
A more informed routine.
The 2025 FITTER Forward recommendations, published in Mayo Clinic Proceedings, explain how devices, skin, and technique work together. Use this guide to prepare for a demonstration with your pharmacist or clinician.
01 / Pens & needles
Read the millimeters.
Closest to 5 mm
Check the millimeter length printed on the box. FITTER Forward accepts 5 mm as an alternative; it is not the same length as 4 mm. Have a clinician confirm the angle and whether you need a skin lift.
Two different measurements
A higher gauge number means a thinner needle. Length determines depth. Confirm that the needle is compatible with your exact pen; these recommendations do not tell you how to fill an empty pen or cartridge.
FITTER Forward · Figure 1
View the anatomy figure at the source ↗Figure 1 carries a separate CC BY-NC 4.0 credit, so TCW links to the original.Where the needle should reach
The original compares skin, underlying fat, and muscle at different body sites.
FITTER Forward · Figure 2
The device, the person, the technique
A closer look at the factors behind comfortable, consistent insulin delivery. The temperature and device details shown are insulin-specific; use your own product instructions.
02 / Sites & skin care
Give each spot a break.
Use only the injection areas permitted for your medication. Rotate within and between those areas, and avoid lumps, thickened tissue, damaged skin, or irritated spots. The map below is an insulin example; its weekly schedule is not a dosing schedule for other medicines.
FITTER Forward · Figure 3
A plan for site rotation
FITTER Forward recommends at least 1 cm between insulin injection points and a consistent rotation pattern. Ask your care team to mark the appropriate areas for your treatment.
Changes in your skin deserve a review.
Tell your clinician about persistent lumps, unusual pain, repeated bruising, bleeding, or leakage. With insulin, moving from thickened tissue to healthy tissue can change absorption and lower glucose; arrange monitoring and dose guidance with your care team.
03 / The daily routine
Know your pen before you use it.
Confirm the label and the device
Check the medication, concentration, prescribed dose, expiry, and appearance against the instructions. Have a pharmacist demonstrate your exact pen and needle. Do not infer a dose from clicks or transfer instructions from a different pen.
Prepare as directed
Wash your hands and use a clean area. For pens that use detachable needles, attach a new sterile compatible needle and remove the required covers. Prime only as the device instructions direct; single-dose autoinjectors may work differently.
Follow the device’s completion cues
Use your taught injection technique and the specified hold time. Hold times and completion signals vary by product. If medication leaks or delivery seems incomplete, contact your pharmacist before repeating a dose.
Finish with safe disposal
Follow the device instructions for removing a detachable needle. Put used sharps immediately in an FDA-cleared sharps container. Never share a pen, even with a new needle. Store the device as labeled.
Technique: FITTER Forward, section 2 ↗ · Disposal: FDA sharps guidance ↗
FITTER Forward · Figure 4
Choose a device that fits your life
Bring your questions about grip, vision, needle anxiety, travel, or cost. A hands-on demonstration and a chance to show the technique back can reveal what needs adjusting.
Read the evidence
The source behind this guide
Klonoff DC, Berard L, Franco DR, et al. Advance Insulin Injection Technique and Education With FITTER Forward Expert Recommendations. Mayo Clin Proc. 2025;100(4):682–699. doi:10.1016/j.mayocp.2025.01.004 ↗
© 2025 The Authors. Published by Elsevier Inc on behalf of Mayo Foundation for Medical Education and Research. Article and figures 2–4 licensed under Creative Commons Attribution 4.0. TCW wrote the surrounding summaries and added its own layout; the reproduced figures retain their original content and captions. Figure 1 is linked separately because its credit specifies a noncommercial license. No endorsement of TCW is implied.
Read the full article in Mayo Clinic Proceedings ↗Field note 03
Storage & handling
There is no universal “peptide storage rule.” The product label or dispensing pharmacy instructions outrank internet charts, general timelines and habits from a different medication.
Unreconstituted
Dry powder / lyophilized
- Keep it in the original labeled container.
- Protect it from heat, light and moisture.
- Refrigerate only when the product-specific instructions require it.
- Research vials may have no validated stability data at all.
Reconstituted or opened
Solution in the vial
- Follow the exact label for temperature and beyond-use date.
- Write the reconstitution/open date on the label when instructed.
- Do not freeze unless the product instructions explicitly allow it.
- Do not use if sterility is questionable, or appearance changes unexpectedly.
Cold-chain awareness
Shipping & excursions
- Refrigeration is common for injectable GLP-1 products, but not universal to every product here.
- “Cool” is not a temperature record; check the package instructions.
- Avoid direct contact with ice packs when freezing would damage the product.
- If a shipment arrives warm when refrigeration is required, contact the dispensing pharmacy before use.
FDA has received complaints about injectable GLP-1 products arriving warm or with inadequate refrigeration. FDA storage guidance ↗
Field note 04
Reconstitution 101
A sterile preparation step, not a kitchen recipe. Reconstitute only when a licensed clinician, pharmacist or the approved product instructions tell you exactly what diluent, volume, concentration and technique to use.
The safe baseline
- 01
Verify the product instructions
Confirm the exact medication, diluent, final concentration, storage condition and beyond-use date.
- 02
Use sterile, single-use supplies
A new sterile needle and syringe are required for every vial entry and every injection.
- 03
Keep critical parts clean
Use a clean work area, disinfect vial stoppers as directed, and never touch sterile connection points.
- 04
Label and dispose
Record the requested date/concentration and place used sharps directly into an appropriate sharps container.
Supplies, translated
3 mL syringe
A capacity, not a dose. It may be used for transfer or reconstitution when the instructions call for that volume.
1 mL syringe
Smaller capacity with finer markings. It can support accurate measurement—but only after the concentration and prescribed volume are known.
Bacteriostatic water
A sterile prescription diluent containing benzyl alcohol. It is not a universal default and should be used only when the medication instructions permit it.
Alcohol prep pads
Use a labeled medical product as directed. Let the stopper or skin dry after preparation; do not improvise with household wipes.
Marketplace rule
Anything that touches an injectable product should be sterile, properly labeled and sourced from a licensed pharmacy, clinician or established medical supplier. General organizers can come from anywhere; sterile supplies should not be a gamble.
Delivery formats
Same destination.
Different error points.
Prefilled pen / auto-injector
Manufacturer-set concentration and device instructions. Use only the exact product’s instructions for use.
Prefilled syringe
Prepared volume in a single device. Verify the label and do not transfer it to another container unless instructed.
Vial + syringe
More measuring decisions and more opportunity for unit/concentration errors. Confirm the prescribed volume with the pharmacist or clinician.