A FlexPen is a pre-filled, disposable insulin pen made by Novo Nordisk. It holds 300 units of insulin in a 3 mL cartridge and lets you dial in precise doses from 1 to 60 units per injection, in single-unit increments. Think of it as a simpler, more portable alternative to drawing insulin from a vial with a syringe.
How a FlexPen Works
The FlexPen uses a dial-a-dose mechanism. You twist the dose selector at the end of the pen to choose how many units you need, and a small window displays the number. Once you’ve dialed your dose, you press the push button to inject. The pen clicks as you turn the dial, giving you both visual and tactile confirmation of the dose you’ve set.
Before each injection, you need to “prime” the pen by dialing two units and pressing the button with the needle pointing upward. This step, sometimes called an air shot, pushes out any air trapped in the needle and confirms that insulin is flowing properly. You should see a drop of insulin at the needle tip before injecting.
Medications Available in FlexPen Form
Several Novo Nordisk products have been packaged in the FlexPen system. NovoLog (a rapid-acting insulin used around mealtimes) and Novolin N (an intermediate-acting insulin) are two well-known examples. Levemir, a long-acting insulin, and Victoza, a non-insulin medication for type 2 diabetes, have also used this delivery format. The pens typically come in boxes of five, each containing 300 units.
FlexPen vs. Vial and Syringe
The FlexPen was designed to solve several real problems with traditional vial-and-syringe injections. Drawing insulin from a vial requires estimating the correct amount by reading tiny markings on a syringe, which introduces dosing errors, especially at low doses. Studies have shown that the FlexPen delivers low, medium, and high doses significantly more accurately than a vial and syringe.
Beyond accuracy, the pen format reduces the social friction of injecting insulin in public. There’s no need to pull out a vial and syringe at a restaurant or office. The pen looks more like a marker than medical equipment, and the injection itself is quicker. In patient studies, people found the FlexPen easier to use than vial and syringe, and the convenience improved adherence to insulin schedules.
FlexPen vs. FlexTouch
Novo Nordisk later introduced the FlexTouch pen as an upgrade. The biggest mechanical difference is in how the injection button works. On the FlexPen, the push button extends outward as you dial up a larger dose, meaning you push it a longer distance for bigger doses. The FlexTouch eliminated this with an internal spring mechanism: the button stays flush at every dose, and the spring does the work of delivering the insulin rather than your thumb pressure. This makes the injection force consistent whether you’re taking 1 unit or 80 units.
The FlexTouch also added a few quality-of-life features: an audible click when the full dose has been delivered, a maximum dose of 80 units (compared to 60 on the FlexPen), and a colored cartridge holder that makes it easier to distinguish between different insulin types at a glance.
Compatible Needles
The FlexPen works with NovoFine disposable pen needles, which also fit most other diabetes pens. These come in several sizes:
- 4 mm, 32 gauge: the shortest and thinnest option, often recommended for lean adults and children
- 6 mm, 31 or 32 gauge: a common middle-ground choice
- 8 mm, 30 gauge: a longer needle, also available in an “Autocover” version with a safety shield
Higher gauge numbers mean thinner needles. A 32-gauge needle is thinner than a 30-gauge. You attach a new needle before each injection and remove it after, so the pen stays capped between uses.
Storage Guidelines
An unopened FlexPen should be stored in the refrigerator between 36°F and 46°F. Once you start using a pen, it can stay at room temperature (59°F to 86°F) for up to 28 days. After 28 days at room temperature, any remaining insulin should be discarded even if the pen isn’t empty. Never freeze a FlexPen, and keep it out of direct heat or sunlight.
Safe Disposal
After each injection, remove the needle and place it immediately into a sharps disposal container. If you don’t have an FDA-cleared sharps container, a heavy-duty plastic household container like a laundry detergent bottle works as a substitute. Never toss loose needles into regular trash or recycling bins, and never flush them. Once the pen is empty, the pen body itself can go in regular household trash after the needle has been removed and properly disposed of.