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Details about Injection Pens

Updated: Dec 9, 2021

Insulin Dosing Pens – Why Use Them?

Pens have greater dose accuracy compared to insulin syringes, especially with low doses of insulin. In all accuracy studies syringes tend to overdose low volumes of insulin. Casella et al. demonstrated that pediatric nurses when attempting to deliver a 0.5 U syringe dose on average drew up a 95% overdose.17,18 In a study where over thirteen hundred diabetics compared pens to insulin syringes, 90% of people reported no or minimal pain with the pen injection compared to 50% using standard syringes.19 In the same study 92% of pen users thought the pens were easy to use compared to 39% of syringe users and 91% would recommend pens to others.

What Pens Are Available?

Once an appropriate insulin type has been selected based on the specific requirements of the diabetic patient then syringes and vials or pen devices and cartridges can be chosen. Caninsulin/Vetsulin® is the only veterinary insulin product that also has an insulin pen for veterinary patients. Two pens are available, a maximum 8 U/dose VetPen® (0.5–8.0 U) with dosing increments of 0.5 U, and a maxium16 U/dose VetPen® (1–16 U) with dosing increments of 1 U. The pens are plastic, but reusable, and have been tested up to 3000 uses, which would be over 4 years in a diabetic receiving twice daily insulin. Insulin cartridges should be discarded after 6 weeks of use. It is recommended that the needle is kept in the skin for 5 seconds during dosing with VetPen®. There are many pens available for human patients with features that may provide benefit for dogs and cats such as 0.5 U increments, memory, and large dials for people with visual or dexterity impairment. Refer to the table for the reusable and disposable pens available to use with human insulin products.

Pen needles are usually between 29 and 32 gauge and come in differing lengths ranging between 4 mm and 12.7 mm. The current recommendation in human medicine favors the shorter pen needles; however the longer 10–12.7 mm needles are recommended for veterinary patients. The technique used for subcutaneous injection is different for dogs and cats compared with people and so, if the needle is too short for veterinary patients, there is risk of intradermal insulin delivery. Once insulin vials are loaded into a pen or a prefilled pen is in use they should generally be stored out of the refrigerator at room temperature less than 25°C or 77°F and away from light. However, manufacturer’s instructions vary and should always be followed. It is recommended to discard most vials after 28 days or earlier if they become discolored. It is important that all users refer to individual product inserts for specific recommendations, as some insulin preparations recommend vials be discarded after as little as 10 days or up to 42 days.

Tips and Tricks for Improving Compliance

Insulin dosing pens all function in a similar manner, although there are minor differences. Manufacturers provide useful written instructions that can be used as a guide during the consultation and later referred to by owners at home. The following check list may also be used when instructing owners on use of the pen.

1.  Familiarize with the components of the pen, including the operation of the dose selector dial and the release trigger.

2.  Practice one-handed operation of the pen. For most people, the most comfortable approach is to hold the pen against the palm with the four fingers and then use the thumb to press the trigger.

3.  For reusable pens, load an insulin cartridge into the pen. This step is not necessary with prefilled insulin dosing pens.

4.  Always mix the insulin before each injection, typically by rolling the pen 10 times and then inverting the pen 10 times. This is crucial for insulin suspensions such as Caninsulin/Vetsulin® (MSD Animal Health), but also advisable for solutions such as Lantus® (glargine) insulin (Sanofi).

5.  Prime the insulin dosing pen. Attach the needle onto the pen, use the dose selector to dial the priming dose of either 1 or 2 U according to the manufacturer’s instructions, hold the pen vertically with the needle upwards, and push the release button. The goal is for a stream of insulin to be ejected from the needle tip. If a stream is not seen, the pen must be primed again until this is achieved. Pens might need to be primed several times when an insulin cartridge is first inserted. This process ensures there is no air in the system and provides reassurance that the pen is working properly.

6.  Practice operating the pen with the dose that will be prescribed for the pet. Use the dose selector to dial the recommended dose and then use a one-handed grip of the pen to push the release trigger. It can be helpful to advise the owner to note the time taken for the pen to deliver the dose as this provides a practical guide for how long the needle must be left in the animal’s skin during injection.

7.  Finally, observe the owner’s technique as they administer their first injection with the insulin dosing pen. Counsel against rushing the process by recommending that four successive steps are used: 1. Gently pinch up the pet’s skin, 2. Slide the needle through the skin, 3. Press the release trigger, 4. Withdraw the needle.

8.  Check that the dose selector dial has returned to the ‘0’ position, which confirms that the full insulin dose was delivered. Note that it is normal for a drop of insulin to be seen on the needle tip after removing the needle from the injection site. There is no need to be concerned that the full dose was not delivered if the drop is seen.


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