Pens and needles
It has been estimated that world-wide around 7.5 billion disposable needles are used outside a medical setting to treat diabetes and other conditions requiring self-administration of injected drugs. Insulin pens are generally preferred by patients but are tied to the use of specific (and more expensive) brands of insulin, supplied in specially made cartridges. Plastic syringes and needles can be used with any insulin supplied in a standard vial. These are recommended for single use only by the manufacturers, but in practice both are frequently re-used by people with diabetes for reasons of convenience and economy. This article reviews practical aspects of insulin administration and delivery, with special reference to resource-poor settings, and considers problems associated with faulty injection technique, the evidence for and against single use of needles, potential problems with storage, and some of the health and environmental hazards associated with disposal of insulin needles.
Insulin needles used during the first 50 years of insulin therapy were intended for repeated use; in some cases patients were provided with a pumice stone with which to sharpen them. They were used with glass insulin syringes which were stored in methylated spirit and boiled periodically to ensure sterility.
New technologies introduced in the 1980s produced much sharper needles with siliconized tips designed to reduce friction as they are pushed through the skin, and attached to plastic syringes. About 7.5 billion are used each year . First generation needles were detachable, allowing reuse of the syringe, but these were soon followed by single unit devices in which the needle was fused with the syringe. Insulin pen devices came into wide use in the 1990s. These are produced by manufacturers to accommodate their own branded insulin cartridges, and come provided with a range of detachable or fixed needles. The introduction of disposable needles and syringes has contributed enormously to the comfort and convenience of insulin administration.
The Insulin Injection
The start of insulin therapy represents a major rite of passage for people with diabetes, and injections constitute a major burden. Intensified therapy, for example, typically involves 4 daily injections, or 1460 injections in the course of a year. People treated with insulin should reasonably expect relatively painless injections and trouble-free injection sites. This can be achieved by combining correct technique – which needs careful instruction – and the use of the right equipment.
Three main types of local reaction may occur at injection sites: lipodystrophy, lipohypertrophy and infection. Lipodystrophy, now largely consigned to history, was an allergic type of reaction to impure insulin. Lipohypertrophy is now much rarer than it was, and is generally due to poor injection technique, usually repeated injections into the same spot. Infections are also exceptionally rare, probably because very few cutaneous bacteria are carried under the skin by the tip of a needle. For this reason, infections due to pyogenic bacteria are generally associated with poor hygiene, and special measures such as the use of alcohol swabs are considered unnecessary when the injection site is acceptably clean.
US online retailers offer single-use syringes in packs of 90 at a cost of $20.99, or 23 cents per unit. [http://www.americandiabeteswholesale.com/catalog/insulin-syringes_178.htm]. In this example, a patient who purchases these syringes, injects twice daily, and disposes of each unit after single use incurs health costs of $167.90 per annum.
Syringe Size and Needle Length
Insulin is manufactured at a standard strength of 100 units/ml (referred to as U100) and standard syringes are manufactured in 30, 50 and 100 unit sizes. U500 insulin is available for patients with a very high insulin requirement. Needles are available at three differing gauges: 28G, 30G and 31G (the higher the gauge, the thinner the needle). Needles are also available in 4, 6, 8 and 12.7 mm lengths. The main potential disadvantage of the longer needles is that these may pass through subcutaneous fat to deliver an intramuscular injection, which is both more painful and more rapidly absorbed. For this reason short (4-6 mm) needles injected perpendicular to the skin are preferred in infants and children. The potential disadvantage of the shorter needles is leakage of insulin, which can be avoided by allowing the insulin to disperse before withdrawing the needle. Most adults, including the overweight, manage well with a 6-8 mm needle.
As with home blood glucose monitoring, the use of pen injectors for diabetes was pioneered by physicians and patients, and was regarded with some suspicion by commercial entities. The pen was pioneered by Drs Sheila Reith - mother of a child with diabetes - and John Ireland in Glasgow. The first pen was built around a plastic syringe and written up in the Lancet in 1981. The first commercial product, Penject, was produced in 1982. The pen simplified life with diabetes for millions of people, but its inventers are rarely remembered for this achievement. Although disposable pens are available, most users with reusable pen devices also reuse the needles.
Novo-Nordisk was the first manufacturer to make full use of the potential of pen devices, but all manufacturers now manufacture attractive pens to fit their own insulin cartridges. This is important for marketing, since many users are more interested in the design of their pen than in the type of insulin it contains, and choice of pen thus dictates the type of insulin.
Guidance provided by the American Diabetes Association stresses the advice provided by the manufacturers but does not prohibit repeated use. In contrast, a more recent systematic review recommends single use only, but provides little supporting evidence.
Infection is a potential hazard of reuse, and the ADA guidance points out that “most insulin preparations have bacteriostatic additives that inhibit growth of bacteria commonly found on the skin. Nevertheless, syringe/needle reuse may carry an increased risk of infection for some individuals. Patients with poor personal hygiene, an acute concurrent illness, open wounds on the hands, or decreased resistance to infection for any reason should not reuse a syringe or pen needle”.
Bending or hooking of the tip of the needle is an additional concern, especially with use of the finer (30G or 31G) needles. This has the potential to cause microscopic tears in the skin or to shed tiny fragments of metal. There are no confirmed adverse consequences of this, and the claim that needle reuse might promote lipohypertrophy is unsupported by systematic evidence. It would however seem prudent to use the stouter (28G) needles if reuse is contemplated.
Few studies have addressed reuse of disposable needles. Schuler and colleagues observed 20 patients who reused pen needles routinely for administration of 33,000 injections without ill-effect. Culture of needles revealed only one instance of bacterial contamination, and there were no instances of clinical infection. The authors concluded that reuse of needles was simple, safe and cost-beneficial. A shorter study demonstrated that reuse of needles for up to 5 times did not increase pain intensity experienced by blinded volunteers, and electron microscopic inspection of 123 needles used 4-5 times showed no evidence of needle tip deformity. The authors estimated that reuse of needles in Europe could save up to EUR 100 million yearly.
For understandable reasons, cost and liability included, the manufacturers have strongly advocated single use of needles, and at one time published electron micrographs of needle tips that had purportedly been blunted by repeated use. An independent group of investigators attempted to reproduce these findings without success in patients making repeated injections. Similar results were however obtained by stabbing the needle into the base of a metal lamp, and the investigators enquired whether Robocop had diabetes?
In practice, many patients do reuse needles, only discarding them (as with a razor blade) when they come to feel blunt. Special care should be taken when recapping the needle, since this may become bent following contact with the side of the plastic sleeve. Needles should be checked before each use and discarded if there are signs of wear. The ADA advises that syringes may safely be stored dry at room temperature, but should not be cleaned with alcohol, which could affect the silicone tip. The syringe should be stored with the tip pointing upwards to prevent blockage of the needle.
The major hazard associated with the widespread use of needles is cross-infection, and this constitutes an added jeopardy when the first user might also be a carrier of HIV or hepatitis. There is the added risk that addicts might purloin used insulin syringes for their own use. Every precaution should therefore be taken to ensure that others are protected from contact with a used insulin needle.
Unfortunately, even basic precautions have been ignored in some resource-poor environments, in which needles may simply be thrown into garbage sacks. Patients should therefore receive the education and the necessary means to dispose of needles safely.
^ Gold K. Analysis: the impact of needle, syringe and lancet disposal in the community. Journal of Diabetes Science and Technology 2011;5(4):848-50
^ Lo Presti D, Ingegnosi C, Strauss K. Skin and subcutaneous thickness at injecting sites in children with diabetes: ultrasound findings and recommendations for giving injection. Pediatr Diabetes 2012;13(7):525-33
^ Paton S et al. (1981) Convenient pocket insulin syringe. Lancet 1(8213):189-90
^ Elliott R. (2014) The pen's mightier... Diabetes Balance July-August, pages 13-15
^ ADA Position Statement: Insulin administration. Diabetes Care Jan 2004;27 (Suppl 1) S106-S109
^ Frid A et al. The third insulin injection technique workshop in Athens (TITAN). Diabetes and Metabolism 2010;36 (Suppl 2), 19-29
^ Schuler G, Pelz K, Kerp L. Is the reuse of needles for insulin injection systems associated with a higher risk of cutaneous complications? Diabetes Res Clin Pract 1992;16:209-12
^ Puder JJ et al. Using pen needles up to 5 times does not affect needle tip shape nor increase pain intensity. Diabetes Res Clin Pract 2005;67(2):119-23
^ Berger B et al. Has Robocop got diabetes? Diabetes Care 2004;27:1851
^ Ishtiaq O et al. Disposal of syringes, needles, and lancets used by diabetic patients in Pakistan. J Infect Public Health 2012;5(2):182-8