Prescribing nurse: Getting to grips with insulin

The introduction of insulin therapy in primary care, once almost unheard of, is now fairly commonplace and it often falls within the remit of practice nurses but there is never one right and one wrong answer when it comes to starting insulin

The best treatment for patients is arrived at taking many factors into consideration including their weight, age, state of general health, personal preferences and coexisting morbidities.¹ This is no less true when it comes to initiating insulin in patients with type 2 diabetes (T2D). For this reason it is an area where the nurse who gets to know her practice diabetes population can be an invaluable resource both for patients and for the primary care team. Those who take on this work will usually have done added training in diabetes, and in most areas there is also recourse to a specialist diabetes nurse.

The introduction of insulin in primary care needs to involve active dose titration, a structured educational programme, continuing telephone support and annual care planning including an agreed target HbA1C.² It also involves frequent self-monitoring by patients who need to learn to adjust doses, understand diet and nutrition, manage hypoglycaemic episodes and acute changes in blood sugar levels, manage injection sites and technique and manage sick days.

NICE2 recommends that insulin initiation is taken on by health care professionals who can demonstrate training and appropriate CPD in the area.

NORMAL INSULIN SECRETION

Prescribing insulin becomes more logical when the normal physiological processes are understood. Normal basal glucose release by the liver is pretty constant throughout day and night so a steady release of baseline insulin is needed to manage this. On top of this basal secretion there is then a surge or bolus of insulin released every time the patient eats. How long this is needed for depends on what is being eaten. There is also an added demand if they are ill, or if they have renal impairment.

Insulin dosage aims to supplement the body's own insulin in order to produce these natural patterns.

WHO NEEDS INSULIN?

Patients need insulin if they either cannot produce enough insulin of their own, or if they have become resistant to it. Ultimately they need both basal insulin and extra peaks to cover the post prandial glucose surge, but initially it can be sufficient just to supplement the basal insulin and allow the patient's system to do the rest.

Some patients resist the idea of insulin, commonly because of concerns about injecting, weight gain, risks of hypoglycaemia and employment issues (particularly in those who drive for a living).

Some patients may stand to lose more than they gain from insulin - for example, the very elderly with a short duration of diabetes who may be unlikely to develop significant disease complications in their lifetime - although there are many elderly people who manage on insulin therapy very well - and those of very high BMI who might be considerably worse off if their weight increases further.

The ideal time to start insulin is when it is the best therapy for the patient because:

• Glycaemic control is off target for the patient
• It will improve glycaemic control above that which can be achieved with other therapy
• It is appropriate to the patient's age, level of fitness, employment, attitude and understanding.

INSULIN TYPES

Human Insulin

Human insulin is synthetic insulin, which is laboratory grown and is available in two forms, a short acting (regular) form (e.g. Humulin S, Actrapid) and an intermediate acting (NPH) form (e.g. Humulin I, Insulatard) as well as premixed fixed dose combinations (e.g. Humulin Mix 25, Humulin Mix 50)

Analogue insulin

This modified version of human insulin is available in two main forms, rapid acting (Humalog, NovoRapid) and long acting (Lantus, Levemir), and in premixed combinations (Humalog Mix 25, 50 NovoMix 30, Insuman Comb 15, 25, 50).

Animal Insulin

Until the 1980s, animal insulin was the only treatment for patients who required insulin therapy.

It is taken from the pancreas of animals, usually pigs (porcine insulin) and cows (bovine insulin) then purified, which reduces the chance of the user developing a reaction to the insulin.

There is some controversy over the benefits and disadvantages of animal insulin compared with human insulin. There have been claims that human insulins may cause behavioural changes, lethargy and loss of hypo symptoms.³ However, no research has been carried out to provide conclusive evidence to either back up or dismiss the claim.

MODE OF ACTION

There are a variety different insulin types in terms of modes of action :

• Rapid acting analogue insulins e.g. NovoRapid with an onset within 5 - 15 minutes
• Short acting human insulins, with fairly fast onset (30 minutes) and short length of action e.g. Actrapid
• Intermediate basal human insulins with a peak in activity e.g. Insulatard
• Long acting basal analogue insulin without a peak (Lantus and Levemir)

The range of activity of these insulins is shown in Box 1.

Rapid Acting Insulin

Rapid acting insulins (e.g. Humalog, NovoRapid) are usually taken just before or with a meal. They act very quickly to minimise the rise in blood sugar that follows eating. They are commonly prescribed to people with type 1 diabetes, but can be prescribed for type 2 diabetes as well.

As rapid acting insulins act very quickly (within 10-15 minutes), care should be therefore taken when administering. They should be used in immediate relation to a meal to avoid hypoglycaemia. They may be injected before a meal, and sometimes immediately after, to ensure strict control of post-prandial levels.

Short Acting Insulin

Short acting insulin is not as quick as rapid acting insulin, and will usually be taken approximately 30 minutes before meals to allow time for their onset of action - one reason for the growing popularity of analogue insulins, which don't require patients to wait as long after injecting before eating.

Intermediate Acting Insulin

Intermediate acting insulins are often taken in conjunction with a short acting insulin. They start to act within the first hour of injecting, followed by a period of peak activity lasting up to 7 hours.

Long Acting Insulin

Long acting insulin may be prescribed for a number of different types of diabetes. Long acting insulin comes in animal and analogue forms. Activity can last up to 24 hours with the exception of bovine PZI which lasts up to 36 hours.

Long acting analogue insulins have no peak activity as such, which allows for a consistent delivery of activity through the day. They may be injected either once or twice daily.

They include Lantus (glargine) and Levemir (detemir), both analogue insulins which have a consistent activity from within an hour after injecting up to 24 hours, and are usually injected once daily. It is difficult to assess the efficacy of long-acting insulins in patients with T2D who are still producing some endogenous insulin.

TYPICAL REGIMENS

Patients typically will stop their oral hypoglycaemic agents when they start insulin, but NICE2 now recommends that most oral hypoglycaemic agents (OHAs) - apart from glitazones - are continued, particularly metformin which carries metabolic benefits.

Typical insulin regimens¹ when starting insulin in T2D include:

• Once-daily intermediate-acting insulin (NPH insulin) plus OHAs - effective for people who are insulin-resistant due to obesity. Once-daily intermediate acting insulin given at bedtime is particularly appropriate for patients whose overnight glucose is high, indicating low levels of basal (endogenous) insulin.
• Twice-daily pre-mixed insulin plus OHAs can be effective for people with significant hyperglycaemia after meals. Consider twice-daily biphasic human insulin (pre-mixed) if HbA1c > 58 mmol/mol (7.5%) on a once-daily intermediate-acting preparation. Consider pre-mixed preparations of insulin analogues (including short-acting insulin analogues) rather than pre-mixed human insulin preparations if:

- immediate injection before a meal is preferred, or
- hypoglycaemia is a problem, or
- blood glucose levels rise markedly after meals, or
- for patients who do not want to/cannot manage complex multiple daily injections.

• Long-acting peakless insulin in the morning (or whenever is convenient, provided it is taken at the same time each day) plus OHAs can be used where the person has high blood glucose during the day and at night, and - would otherwise need twice-daily basal insulin injections in combination with oral anti-diabetic '² NICE also suggests this regimen - for those who require assistance from a carer or health care professional to administer their injections, because it does not have to be given at a particular time of day.² It is also useful for people who are reluctant to consider insulin therapy, as there is only one daily injection involved.

Consider switching to a long-acting peakless insulin from NPH insulin^4,5 if the person:

- does not reach target HbA1c because non-compliance with more frequent insulin administration, or

- has significant hypoglycaemia with NPH insulin irrespective of HbA1c level, or

- needs help to inject insulin and could reduce the number of injections with a long-acting analogue.

MATCHING THE REGIMEN 
TO THE INDIVIDUAL

For every person, there will be a range of possible treatments and no single 'right' choice. Whichever option is chosen, there must always be a clear rationale behind the decision. Here are some considerations:

Basal with OHAs may be a good choice for people

• Who are overweight and insulin resistant
• Who are reluctant to start insulin (for example, due to needle phobia - although genuine needle phobia is very rare)
• Who are unable to inject themselves.

Twice-daily pre-mixed insulin may be a good choice for people:

• With fairly regular lifestyles, who eat similar amounts at similar times each day
• Who need to optimise blood glucose control because of complications, illness or a wound.

Baseline with mealtime dosing tds is most often used in Type 1 diabetes but may be a good choice for people who

- are highly motivated towards good control

- have a good understanding of diet and diabetes

- have variable diets and activity levels

- are prepared to adjust their dose on a daily basis
- who need flexibility because of an erratic lifestyle, shiftwork, regular travelling across time zones, or regular sport.

The brand of insulin will usually depend on what kind of injection device the person prefers.

FIRST APPOINTMENT

FIRST INJECTION

Preparing the way - dummy injections

Many people think they will have to use a large needle, and inject into a vein. It's important to allay their fears, and show them how easy and relatively painless injecting can be. Do this as soon as possible! Ask the person to simply insert the needle for a 'dry run'. It can be very reassuring for people to try this soon after diagnosis, long before insulin treatment is actually required.

The first appointment

As a general guide, you should allow between half-an-hour and an hour for the first injection appointment. Ask the person to choose a time when they will not need to drive for a few days. Some may wish to postpone it until after a holiday, or after Ramadan, when their usual routine is disrupted.

They may wish to bring a partner or friend.

• Discuss the need to carry on taking OHAs. NICE recommends continuing metformin, if tolerated2
• Refer them to a dietitian for a full dietetic appraisal if this has'nt already been done.
• Refer to a structured education programme - XPERT is recommended for people taking insulin
• Provide a contact number for advice.

Ideally, the first injection would be near the beginning of the week so the person is fairly confident before the weekend, when you would be unavailable if they had any problems. Telephone them the day after their first injection, and see them as often as necessary, gradually spacing out the appointments as their confidence grows.

GETTING THE START DOSE RIGHT

There is no need to go in heavily. Sending the patient hypo on day 1 will not encourage their confidence levels. The correct dose can be hard to predict than in T2D, as type 2 patients tend to be resistant to (as well as absolutely or relatively deficient in) insulin and the relative contribution of each factor will vary.

You should aim for a gradual improvement in blood glucose levels. Sudden normalisation of long-standing high blood glucose can sometimes cause progression of diabetic retinopathy, insulin neuritis or 'pseudo hypos' (hypo symptoms at normal glucose levels).

• Once-daily regimens often start with 10 units.
• Most twice-daily regimens start with 6-10 units twice daily, depending upon the person's build.
• There is no such thing as a'correct' dose: starting low and working up will build the person's confidence and your own.

Some other points to remember

Exercise - insulin will be absorbed faster by an exercising muscle. Advise patients not to inject immediately before strenuous exercise, or to reduce the dose.

Temperature - heat speeds up the absorption of insulin. People should avoid injecting immediately before or after a hot bath or shower.

Injecting through clothing should be discouraged.

DOSE ADJUSTMENT

When adjusting the dose involve the patient in decisions and consider adjustments of 10% of the total daily insulin dose at a time. Rate preventing hypos as more important than correcting high blood glucose levels. If the patient is having hypos, reduce doses by 20%.

1. Adjusting twice-daily insulin

The morning dose controls blood glucose levels throughout the day, while the evening dose controls glucose levels after the evening meal and throughout the night. Twice-daily insulin doses can be adjusted from day-to-day, according to the person's planned level of physical activity.

2. Adjusting once-daily insulin

Once-daily insulins such as Lantus or Levemir are designed to work throughout a 24-hour period. Pre- breakfast (fasting) blood glucose levels give a good indication of their effectiveness. After starting insulin treatment (usually with about 10 units daily) the dose should be titrated every 3-7 days until the target is achieved.

3. Adjusting multiple injection therapy

People who add short-or rapid-acting meal-time insulin to their once-daily insulin regimen can continue their current dose of long-acting insulin, and simply include a dose of fast-acting insulin before each main meal.

For those choosing a multiple injection regimen from the start of insulin treatment, try starting with one-third of the daily total insulin dose as long-acting insulin. Divide the remaining two-thirds - the fast-acting insulin - between the three main meals.

Adjust the long-acting insulin to achieve satisfactory pre-breakfast blood glucose levels: reduce the dose if the blood glucose is too low during the night or before breakfast, and increase the dose if glucose levels are too high before breakfast.

Adjust the short-acting insulin to achieve satisfactory glucose levels after meals.

CHOOSING AN INJECTION SITE

There are a number of suitable sites.

Abdomen - fastest absorption, usually plenty of subcutaneous fat. A good option for fast-acting insulin.

Thighs - slower absorption. Best with intermediate- acting insulin, or the evening dose of a twice-daily insulin regimen. Very little subcutaneous fat, so use a pinch up and/or short needles.

Arms - medium-to-fast absorption. Make sure there is sufficient fat, and use short needles.

Buttocks - slowest absorption. Use for intermediate or long-acting insulins. Plenty of subcutaneous fat, so no 'pinch up' is needed, but can be a difficult area to reach for a patient who is self-injecting.

Repeatedly injecting into the same small area results in lumps, which hinder insulin absorption and can be unsightly. Alternate between the left and right side on a weekly basis, and rotate sites within the same area. Patients often reuse sites because they become numb.

INSULIN DELIVERY DEVICES

There are many different types of insulin delivery device available, including syringes, pens, jet injectors, oral insulin and pumps. The choice of device should be made in partnership with the patient bearing in mind factors such as their dexterity and vision, and the maximum doses that the device can carry.

Syringes

Direct subcutaneous insulin injection remains the most common form of delivery, using a needle and syringe. The needle gauge and needle length should be adjusted for comfort.

Pens

Insulin pens are easy to use. Some insulin pens use replaceable cartridges, and others use non-replaceable cartridges and must be disposed of after use.

Most insulin pens use replaceable needles, which have become extremely short and thin. The replaceable cartridges for insulin pens come in 3 and 1¹/2 ml sizes, although 3 is more commonly used. Prefilled insulin pens are disposed of when the insulin within the cartridge is used up.

External Insulin Pumps

People with diabetes can successfully use insulin pump therapy, also known as Continuous Subcutaneous Insulin Infusion (CSII), irrespective of their age and diabetes type.

The pumps are external and deliver constant amounts of rapid- or short-acting insulin via a catheter placed under the skin. In the UK around 1 in 1,000 people with diabetes wears an insulin pump. NICE advises that people with type 1 diabetes should be assessed for their need and suitability for insulin pump provision, but does not recommend them for people with T2D.²

Pumps remain hard to access and expensive, but they are also accurate, precise and flexible, and provide tight blood glucose control. In the UK they are less common than in other countries. Future recommendations are for increased provision, including follow-up, support and education. This may see an expansion in the number of teams and centres that can deliver CSII.

SUMMARY

The practice nurse who wishes to initiate insulin should make sure they have achieved the appropriate competence through attending courses and maintaining CPD.

The initiation of insulin needs to be as part of a structured programme, offering appropriate education and support.

There is considerable guidance around start doses and managing adjustments, but these need to be individually tailored to the individual patient as response to insulin, particularly in type 2 diabetes, can be hard to predict.

The overall best interests of the patient should be weighed up, treatment targets set and the nurse should work with the patient to achieve the best possible outcome.

REFERENCES

1. Starting insulin treatment in adults with type 2 diabetes: RCN Published May 2004 revised March 2006

2. NICE. Type 2 Diabetes (CG66). Available at: http://guidance.nice.org.uk/CG66 Accessed June 2012

3. Philis-Tsimikas A, Charpentier G, Clauson P, Ravn GM, Roberts VL, Thorsteinsson B. Comparison of once-daily insulin detemir with NPH insulin added to a regimen of oral antidiabetic drugs in poorly controlled type 2 diabetes Clin Ther 2006;28(10):1569-81.

4. Cochrane Summaries. Long acting insulin analogues versus NPH insulin (human isophane insulin) for type 2 diabetes mellitus. October, 2009. Available at: http://summaries.cochrane.org/CD005613/long-acting-insulin-analogues-versus-nph-insulin-human-isophane-insulin-for-type-2-diabetes-mellitus. Accessed June 2012.