Monday, July 16, 2007

Insulin pen - managing diabetes

An insulin pen (or just "pen") is an insulin delivery system that

  1. generally looks like a large pen,
  2. uses an insulin cartridge rather than a vial, and
  3. uses disposable needles.

Pens are the predominant insulin delivery system in most of the world, except the United States, where syringes and insulin vials still dominate. Pens are made by Novo Nordisk, Eli Lilly, Disetronic, and Owen Mumford. Disetronic makes pens for other companies, including Aventis.

Some pens use replaceable insulin cartridges, and some pens use a non-replaceable cartridge and are disposed of after use. All pens use replaceable needles. Most pens use special pen needles (see discussion below), which can be extremely short and thin. The Disetronic pen, however, uses the same syringe as their DTron insulin pump, which has a traditional syringe leuer lock needle.

Pens With Replaceable Cartridges

Pens with replaceable cartridges are made by Novo Nordisk, Owen Mumford, and Disetronic. BD used to make pens, including the BD Pen Mini, but they are no longer making pens.

Insulin cartridges for pens come in 3.0 ml and 1.5 ml sizes, with 3.0 being the predominant size. The 1.5 ml size is being phased out and availability may be limited. Insulin cartridges are made by Eli Lilly, Novo Nordisk, and Aventis.

Prefilled Pens

Pens that come with a prefilled insulin cartridge are thrown away when the insulin is used up. Prefilled pens are sold by insulin makers Eli Lilly, Novo Nordisk, and Aventis. Lilly only sells prefilled pens which come with a variety of Lilly insulins, including HUmalog, Regular, NPH, and various mixes, including Humalog mixes. Novo Nordisk sells both prefilled pens and pens that take replaceable insulin cartridges with Novolog and other Novo Nordisk insulins. Aventis sells prefilled pens with Lantus Lantus and other Aventis insulins. (Lantus pen availability is limited -- Lantus pens are available only in Germany and the UK as of November 2002.)

Prefilled pens using pre-mixed insulin are usually marketed for use by people with type 2 diabetes. The fixed ratio of insulins does not provide the flexibility needed to accommodate varying food and exercise.

Dosing with a Pen

Using a pen is quite easy. Once the cartridge is loaded, you simply screw on a pen needle, prime if needed to clear out any air in the cartridge, dial in the desired dose, inject the needle, and press the button to deliver the insulin. If you use a pen with an insulin suspension, such as NPH or a premixed insulin, you will need to gently shake the pen to be sure the insulin is mixed prior to use. Pens are easy enough for kids to use, and are excellent for use at school or while out and about.

Pen needles should be removed after each use to prevent air from entering the cartridge and to prevent insulin from leaking out. There are many different pen needles available, in varying lengths and diameters.

  • BD pen needles come in three lengths: 5mm and 8mm (31G), and 12.7mm (29G)
  • Novo Nordisk pen needles, called NovoFine®, come in 6mm (31G) or 8mm (30G)
  • Owen Mumford pen needles, called Unifine Pentips, come in four sizes: 6mm (30G), 8mm (30G), 8mm (29G), and 12mm (29G)
  • Disetronic pen needles, called Penfine, come in four sizes: 6mm (31G), 8mm (31G), 10mm (29G), and 12mm (29G)

The smallest pen needles are very short and very thin and help minimize the discomfort of injection. Unlike syringes, pens need to be held in place for several seconds after the insulin is delivered to ensure that no insulin leaks out. Syringe users who switch to pens should pay close attention to the injection site and test their blood glucose often as they become accustomed to pen injections.

Dosing increments vary by pen, with some pens starting at 1/2 or 1 unit and allowing 1/2 unit dosing, while others dose in one or two unit increments. While pens offer injection convenience, they don't allow mixing of multiple insulins, so if you inject short and long acting insulin together (e.g., Humalog and NPH), you'll double your number of injections.

Pens offer repeatability in dosing accuracy compared with syringes. Also, because dosing with a pen involves dialing a mechanical device and not looking at the side of a syringe, insulin users with reduced visual acuity can be assured of accurate dosing with a pen.

New "Pen" Devices in New Shapes

Pens have traditionally been shaped like a large pen — hence the name. In recent years, Novo Nordisk has introduced three products that function like pens -- they use insulin cartridges and disposable needles -- but are shaped differently. These devices include the Innovo; the InDuo, which combines the Innovo insulin doser with a LifeScan OneTouch Ultra glucose meter; and the Innolet, a pre-filled device available with N or 70/30 insulins only. The Innovo and InDuo have easy-to-read LCD displays and remember the last dose and how long ago it was delivered, though they can only deliver insulin in increments of one unit. The Innolet uses a dial, much like a kitchen timer, to set the does and can deliver insulin in one unit increments. With young kids, half-unit dosing is essential, so these products are better suited for older kids and adults.

A pen with a memory

In February, 2007, Eli Lilly announced a new concept to the US market: "HumaPen MEMOIR is the first and only insulin pen with a memory. HumaPen MEMOIR records the date, time, and amount of your last 16 doses (including priming doses). You can see exactly when and how much insulin you last took. With HumaPen MEMOIR, you simply "dial" your dose by turning the dose knob in one-unit increments (up to 60 units) after initial set-up. If you dial too many units, you can correct the dose without wasting any insulin. HumaPen MEMOIR is a reusable pen for use only with Humalog (insulin lispro injection [rDNA origin]) 3 mL insulin cartridges."

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