Pen needles

Pen needles are used in conjunction with injection pens to deliver injectable medications into the body.

A pen needle consists of a hollow needle which is embedded in a plastic hub and attaches to injection pens. Pen needles come in a variety of needle lengths and diameters and are used by health professionals and patients for injection of a variety of medications. They are commonly used by people with diabetes who often require multiple daily insulin injections.

Needle technology has changed over the past decades. Many years ago home use syringe needles were large, and had to be sterilized and sharpened by hand by patients themselves. Today’s pen needles are engineered and manufactured for greater comfort and ease of use with electro-polishing for needle smoothness; thin, fine point tips for ease in penetration; lubrication for less friction and more glide; plastic caps for safety; and individual wrapping for sterility. Injection pen and pen needles are an alternative drug delivery method to the traditional vial/syringe method.

Background

Insulin and other injectable medications are commonly administered with drug delivery pens. Pens are one of the easiest and fastest-growing methods for administering insulin and other injectable medication. The medication either comes in a disposable pen or in a cartridge for use with a re-usable pen. The user generally attaches the pen needle, dials a dose of medicine, then injects the medicine under the skin. Highly popular for more than 20 years in Europe, use of injection pens and pen needles is rapidly spreading in the U.S. for diabetes care and other non-diabetes drugs.

As technology and competition advance, driving the desire for more comfortable and more effective injections, the design of the pen needle and its parts has become more and more important. Some of the newest pen needle designs proactively address ease of use, injection flow, ergonomic handling, injection depth control and accuracy, and safe use from transport to disposal.

The advantage of pens and pen needles

Compared to the older vial/syringe method, pens and pen needles are designed for easier, more discreet use, greater convenience and delivery of a more accurate dose. As well, with pens and pen needles you no longer need to push the needle through the rubber vial stopper. Without this step, the tip of the needle better retains its sharpness and lubrication for a more comfortable injection.

Pen needle construction

Pen Needle for Humira (with and without protective caps)

Each pen needle is embedded in a plastic hub that can attach to the pen by means of a twist-on fitting or a click-on.^[1] Two protective caps (outer and inner caps) protect the user and the needle. The peel foil protects the sterility of the needle and holds information such as lot number, and needle length and gauge. Pen needles vary by needle length and diameter(gauge).

Pen needle terminology

There are two main characteristics of a pen needle: gauge (diameter or thinness) and length.

Gauge

The diameter or thinness of a pen needle is measured by its gauge (G). The greater the gauge number, the thinner the needle. The thinner the insulin pen needle, the less pain those receiving the injection may feel.

Length

Length of a pen needle is measured in millimeters (mm). The length of the needle impacts the depth of the injection. An 8 mm needle has been the most common length used with insulin pens, although shorter needles are growing in use.

Pen Needle comparison.jpg

Pen needle availability

There are many different pen needles offered in varying lengths and diameters. Availability of specific lengths and sizes vary by country.

• Allison Medical pen needles branded SureComfort come in six sizes: 4mm (32G), 5mm (31G), 6mm (32G), 8mm (30G & 31G), 12mm (29G)
• Terumo pen needles, called Nanopass, come in 4mm (23.5G or 34G), 6mm (32.5G), or 8mm (32.5G) are one of the thinnest. ^[2]
• Insupen pen needles are available in five lengths: 4 mm, 5 mm, 6 mm, 8 mm, 12 mm and four different gauges including 33G, one of the thinnest in the UK (along the entire length on the cannula).
• Montmed supplies ultra-thin universal pen needles in different lengths: 4 mm, 5 mm, 6 mm and 8 mm, in different gauges. The same company has invented montKiddy colored pen needles for children and young people which helps them to remember to change their pen needle and rotate their injection site.^[3]
• B. Braun Melsungen supplies Omnican fine Pen needles in five lengths: 4 mm, 6 mm and 8 mm (31G), 10 mm (30G) and 12 mm (29G)
• Stat Medical Devices supplies Insulin Pen Needles in three lengths: Micro - 5 mm (31g), Xtra - 8 mm (31g), and Standard 12.7 mm (29g)
• BD Medical (Becton Dickinson) supplies BD pen needles in four lengths: Nano - 4 mm (32g), 5 mm and 8 mm (31G), and 12.7 mm (29G)
• Owen Mumford supplies Unifine Pentips in five lengths: 4 mm (32G), 5 mm, 6 mm and 8 mm (31G) and 12 mm (29G).
• Novo Nordisk pen needles, called NovoFine, come in 6 mm (31G), 6 mm (32G tip) or 8 mm (30G)
• Ypsomed’s Penfine and Clickfine pen needles come in 4.5 mm (31G), 6 mm (31G), 8 mm (31G) 10 mm (29G) and 12 mm (29G).
• UltiCare supplies pen needles in four lengths: 4 mm (32G), 6 mm (31G), 8 mm (31G) and 12 mm (29G). UltiCare packages their pen needles in an UltiGuard Safe Pack that combines needles and an approved sharps container all in one system.
• Cambridge Sensors Ltd. supplies insulin pen needles in three lengths under the Microdot brand: 4 mm (32G), 6 mm (31G), 8 mm (31G)

The smallest pen needles are very short and very thin and help minimize the discomfort of injection. Because of their bigger inner diameters, larger diameter pen needles help large dose volumes to flow more quickly and with less manual strength through the needle. Proprietary Thin-Wall Technology is used by BD Medical to facilitate flow even through the smallest needles with minimal extra force.

Choosing a pen needle

Many factors figure into choosing the appropriate pen needle. Pen needle manufacturers advise that users consult their healthcare professional for advice on choosing the most appropriate pen needle.

Injection Technique

The proper injection technique should be used with the needle length is best for you. Inject straight in or at an angle. Injecting at a 90° angle (vertically) is the most common injection technique. Some people who inject with longer needles insert them at an angle to help avoid injecting in the muscle tissue. For needles longer than 5mm, pinching up the skin can avoid intramuscular injection, which will alter the way the drug is metabolized by the body.

Body Build

A person's build and amount of body fat (subcutaneous tissue) used to be the important element in considering which pen needle length to choose. Body Mass Index (BMI) is one way to calculate the amount of body fat. The CDC ^[4] (Center for Disease Control and Prevention) has a BMI calculator for adults, children and teenagers. Children and thin, young adults may need to choose the shortest needles.

Research by several different companies and clinical experts have demonstrated that the thickness of the skin varies very little from person to person regardless of BMI.^[5] To reach the subcutaneous tissue and avoid the muscle layer, needles as short as 4 mm or 5 mm are effective and more comfortable for most people ^[6][7][8]

A recent review of 157 relevant clinical papers by 127 experts from 27 countries noted that even in obese patients, needles shorter than 8mm have equal efficacy and reduce the chance of an intramuscular injection.^[9]

Compatibility

Compatibility identifies which pen needle can be used with a specific brand of injection or insulin pen. Most pen needle manufacturers design their pen needles for either universal fit or fit with all major injection pen brands, and provide information about compatibility. International standards (ISO) have been established to ensure that a pen needle that meets the standards will fit all pens. It is always best to check with your health care professional to ensure the pen needle you are using has actually been tested with the pen you have chosen.

Attachment

Pen needles can either screw-on or click-on to attach to an injection pen. While most pen needles screw-on to attach, one pen needle made in Switzerland with a patented technology by Ypsomed AG (sold in the US under the name Clickfine), allows the user to either click-on or screw-on the needle to attach.

Using a pen needle that clicks-on to attach may be beneficial for people with arthritis, other manual dexterity issues, or vision impairment.

Some people are afraid to see the actual needle tip penetrate their skin, while others, primarily in hospitals, are concerned about needle-stick injuries when disposing of a pen needle. A device called Autoshield Safety Pen Needles is available from BD Medical (http:www.BD.com/us/diabetes) in 5mm and 8mm lengths. The device hides the needle tip, can be activated only once, then locks the needle tip away.

Dose Size

People taking large dose volumes may chose pen needles with bigger inner diameters. Larger diameter pen needles such as 29g, help large dose volumes flow more quickly and with less manual strength through the needle. Many smaller gauge needles (BD Medical, Franklin Lakes, NJ) use proprietary thin-wall technology, permitting larger volumes to inject through needles as small as 32g.

Where to inject

It is important that injections are given into the proper areas of the body. In general, a health professional determines the best injection site for a patient. There are several recommended injection sites including the abdomen, parts of the buttocks and thigh areas. Health professionals advise that patients keep at least two fingers width (3 cm) away from the navel when injecting.

Common injection sites include:

• Upper side area of the arms
• Abdomen (except area close to the navel)
• Front and sides of thighs
• Upper and outer surfaces of the buttocks

The most reliable and consistent absorption of insulin occurs when it is delivered into the layer of tissue (subcutaneous adipose tissue, or “fat”) located between the skin and the muscle.

Injection Safety Considerations

• Perform an 'airshot' with a few units of medication before giving an injection
• Inject in a place below the skin, but above the muscle (in the subcutaneous tissue)
• Inject slowly according to instructions from a medical practitioner and injection pen instructions − keep the needle in the skin for at least 6 seconds after injecting
• Once the needle has entered the skin surface, do not change the angle of the injection pen. A change in the angle could cause the needle to break or get stuck in the skin
• Change injection sites between injections. If this is not done, tissue hardening may result and lipodystrophy. The use of colored pen needles and assigning each color to different injection sites helps remembering to rotate the injection site.
• Change the needle after each injection. Reusing the needle increase the risk of skin complications and lipodystrophy.In case of forgetting to change the needle with each injection, colored pen needles can be used. Assigning each color to different injection times can serve as a memory aid to ensure single use of the needle.
• Remove the pen needle immediately to prevent air from entering the cartridge and to prevent insulin from leaking out.

Needle disposal

Every year some 1.4 billion insulin syringes are used in the United States.^[10] Accidental needlesticks occur through improper 'pre-disposal' handling and transport of used needles by the patients themselves, their relatives, friends, or medical staff.^[11] Accidents can occur during waste transport and treatment as well as at recycling facilities and landfills. For these victims, each accidental needlestick causes not only a puncture wound but also the fear of possible secondary infection. The risk of accidental puncture wounds can be reduced by properly disposing of the needle in a container marked sharps medical waste. The container should than be taken to a final disposal facility in your local community.^[12][13]

See also

• Clickfine pen needles
• Sharps container
• Sharps waste

References