How to use a NovoRapid FlexPen: a UK patient walkthrough

NovoRapid (insulin aspart) is one of the most prescribed mealtime insulins in the UK. The FlexPen is the disposable, pre-filled pen device the medication usually arrives in. If you have just been switched to it from a vial-and-syringe regimen, or from a different rapid-acting insulin, the device-specific behaviour matters more than the molecule does.

This is a patient-side walkthrough of the NovoRapid FlexPen, anchored to the manufacturer’s Patient Information Leaflet, the EMA Summary of Product Characteristics, and the FIT UK injection-technique recommendations. We are a supplies retailer; clinical decisions about your insulin dose, schedule and titration belong to your diabetes team.

What the FlexPen is

A pre-filled, disposable, multi-dose pen containing 3 mL of insulin aspart at 100 units/mL, that is, 300 units total. The dial selects 1 to 60 units in single-unit increments. Once empty, the entire pen is discarded; it is not refillable.

The FlexPen has been on the market for over twenty years. A newer Novo Nordisk pen, the FlexTouch, replaces it for some users, same molecule, different mechanical action, lower force needed to depress the dose button. Both are still in active distribution as of 2026.

Before first use

Take a new FlexPen out of the fridge at least 30 minutes before you plan to use it. Insulin injected straight from refrigerator temperature is more painful than injection at room temperature, and the cartridge contents are slightly more viscous which can affect dose delivery time.

You will also need:

• One sterile, single-use pen needle, ISO 11608-2-compliant, most adults use 30G or 31G × 4 mm or 5 mm (the FITTER 2016 consensus recommends 4 mm for routine subcutaneous insulin injection)
• An alcohol prep pad or soap and water
• A sharps bin

Step 1, Visual check

Check the appearance through the cartridge window. NovoRapid should be clear and colourless. If it is cloudy, particulate, discoloured or has visible crystals on the inside of the cartridge, do not use the pen, return it to your pharmacy.

This is a common pitfall in the first weeks: people switching from cloudy intermediate-acting insulins (NPH, Insulatard) sometimes assume rapid-acting insulin should also be cloudy. It should not be. NovoRapid is a clear analogue.

Step 2, Attach a pen needle

Remove the pen cap. Wipe the rubber stopper with an alcohol pad. Take a fresh pen needle, pull off the paper tab, and screw the needle straight onto the pen until it is finger-tight. Pull off the outer plastic cap (set it aside, you’ll need it later for safe needle removal) and pull off the inner cap (discard).

If the needle wobbles or won’t seat, it is not threading correctly, back it off and try again. Pen needles do not require force.

Step 3, Prime the pen (“airshot”)

This step is non-negotiable on every injection. The PIL specifies an airshot of 2 units before each dose:

1. Dial 2 units
2. Hold the pen vertically, needle pointing up
3. Tap the cartridge gently with your finger so any air bubbles rise to the top
4. Press the dose button fully down until the dose counter returns to 0
5. A drop of insulin should appear at the needle tip

If no drop appears, repeat. If still no drop after two attempts, change the needle and try again. If still no drop, the pen is faulty.

Why this step trips switching users. Vial-and-syringe regimens do not require an airshot, you draw exactly the volume you need. Pen users sometimes try to skip priming because their old workflow didn’t include it. The pen mechanism has a small dead-space and air can collect at the cartridge top during transport and storage; without priming, your first injection delivers slightly less than the dialled dose.

Step 4, Dial your dose

Turn the dose selector to the prescribed unit count. The dose window confirms the dial visually. The pen also clicks audibly with each unit, which is important for visually-impaired users who depend on the click-count to set the dose by feel.

You cannot dial a dose larger than what’s left in the cartridge. If you try, the dial stops. The PIL describes how to handle a part-cartridge top-up; in practice, most users start a fresh pen rather than splitting a dose across two cartridges.

Step 5, Inject

Pinch up a fold of skin between thumb and index finger, insert the needle at 90 degrees, and press the dose button fully down. Hold for at least 6 seconds after the dose counter returns to 0 before withdrawing the needle. The 6-second hold ensures the full dose enters the tissue rather than tracking back along the needle channel during withdrawal.

For routine 4 mm pen needle use, FIT UK 5th edition recommends injection without a skin pinch in adults, because the 4 mm length cannot reach muscle through the skin layer alone in essentially any adult body habitus. Some patients prefer the pinch for tactile reassurance, that’s fine, but it is not strictly necessary.

Step 6, Remove and dispose

Withdraw the needle. Pick up the outer plastic cap you set aside, slide the needle into it (the “scoop technique”, do not hold the cap with your other hand, to avoid needlestick injury), and unscrew the needle off the pen. Drop the capped needle straight into your sharps bin.

Replace the pen cap on the pen body (without the needle attached). Store the in-use pen at room temperature, below 30 °C, away from direct heat and light. Do not refrigerate an in-use pen, this is a common mistake. Once a NovoRapid FlexPen is in use, the manufacturer specifies room-temperature storage for up to 28 days.

Switching users: what’s different from other pens

If you are coming to NovoRapid FlexPen from a different device, the following are the most-asked-about differences:

• Vs Humalog (lispro) KwikPen: same airshot procedure, same dose window, similar feel. The molecule timing is similar, both are rapid-acting analogues. Dose-for-dose conversion is generally one-to-one but should be confirmed by your prescriber.
• Vs Lantus SoloStar (glargine): completely different, Lantus is long-acting basal, NovoRapid is rapid-acting mealtime. Do not confuse the two pens; different dose schedule, different colour-coded packaging.
• Vs FlexTouch (newer Novo device): the dose button on FlexTouch requires substantially less force to fully depress at high doses. If hand strength is a concern, FlexTouch is worth asking about.

In-use storage and the 28-day rule

The PIL specifies that an in-use FlexPen is stable for up to 28 days at room temperature below 30 °C. After 28 days from first use, any remaining insulin should be discarded, even if the pen is not empty. Date the pen on first use with a marker on the body so you can track this without remembering it.

A 300-unit pen lasts most type 1 adults around 10 to 14 days. The 28-day rule rarely bites in practice for users with substantial daily insulin requirements, they finish the pen first. Lower-dose users (some type 2 patients on small mealtime doses) can hit the limit before the cartridge is empty. The unused remainder is discarded; this is not a failure, it’s expected.

What to do if a dose goes wrong

The Diabetes UK and BNF references cover dose error management in detail and are the right place to read about specific corrective actions. The general pattern: contact your diabetes team if you have injected significantly more than your prescribed mealtime dose; eat carbohydrate and check glucose if you have given a mealtime dose without then eating.

This is one of the points where we deliberately stop and refer outward. Insulin dose errors are a clinical management problem that depends on your specific prescription and your specific blood glucose response. We are not equipped to give that advice and we will not.