Methods of insulin administration

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a. Insulin syringes and needles

Plastic disposable syringes are available in 1-mL, 0.5-mL, and 0.3-mL sizes. The "low-dose" 0.3-mL syringes have become increasingly popular, because many diabetics do not take more than 30 units of insulin in a single injection except in rare instances of extreme insulin resistance. Two lengths of needles are available: short (8 mm) and long (12.7 mm). Long needles are preferable in obese patients to reduce variability of insulin absorption. Ultrafine needles as small as 31 gauge reduce the pain of injections. "Disposable" syringes may be reused until blunting of the needle occurs (usually after three to five injections). Sterility adequate to avoid infection with reuse appears to be maintained by recapping syringes between uses. Cleansing the needle with alcohol may not be desirable since it can dissolve the silicone coating and can increase the pain of skin puncturing.

Any part of the body covered by loose skin can be used, such as the abdomen, thighs, upper arms, flanks, and upper buttocks. Preparation with alcohol is no longer required prior to injection as long as the skin is clean. Rotation of sites continues to be recommended to avoid delayed absorption when fibrosis or lipohypertrophy occurs from repeated use of a single site. However, considerable variability of absorption rates from different sites, particularly with exercise, may contribute to the instability of glycemic control in certain type 1 patients if injection sites are rotated too frequently in different areas of the body. Consequently, it is best to limit injection sites to a single region of the body and rotate sites within that region. The abdomen is recommended for subcutaneous injections, since regular insulin has been shown to absorb more rapidly from there than from other subcutaneous sites. The effect of anatomic regions appears to be much less pronounced with the analog insulins.

b. Insulin pen injector devices

Insulin pens eliminate the need for carrying insulin vials and syringes. Cartridges of insulin lispro, insulin aspart, insulin glargine, regular insulin, NPH insulin, and 70% NPH/30% regular insulin are available for reusable pens (Novo Nordisk, Becton Dickinson, and Sanofi Aventis pens). Disposable prefilled pens are also available for insulin lispro, NPH, 70% NPH/30% regular, 75% NPL/25% insulin lispro, and 70% insulin aspart protamine/30% insulin aspart. Thirty-one gauge needles (5, 6, and 8 mm long) for these pens make injections almost painless.

c. Insulin pumps

In the United States, Medtronic Mini-Med, Animas, and Deltec Cozmo insulin infusion pumps are available for subcutaneous delivery of insulin. These pumps are small (about the size of a pager) and very easy to program. They offer many features, including the ability to set a number of different basal rates throughout the 24 hours and to adjust the time over which bolus doses are given. They also are able to detect pressure build-up if the catheter is kinked. Improvements have also been made in the infusion sets. The catheter connecting the insulin reservoir to the subcutaneous cannula can be disconnected, allowing the patient to remove the pump temporarily (e.g., for bathing). The great advantage of continuous subcutaneous insulin infusion (CSII) is that it allows for establishment of a basal profile tailored to the patient. The patient therefore is able to eat with less regard to timing because the basal insulin infusion should maintain constant blood glucose between meals. Also the ability to adjust the basal insulin infusion makes it easier for the patient to manage glycemic excursions that occur with exercise.

CSII therapy is appropriate for patients who are motivated, mechanically inclined, educated about diabetes (diet, insulin action, treatment of hypoglycemia and hyperglycemia), and willing to monitor their blood glucose four to six times a day. Known complications of CSII include ketoacidosis, which can occur when insulin delivery is interrupted, and skin infections. Another disadvantage is its cost and the time demanded of physicians and staff in initiating therapy.

d. Inhaled insulin

A novel method for delivering preprandial insulin by inhalation has been reported. A 12-week study in type 1 patients showed that inhaled insulin is as efficacious as subcutaneously delivered insulin without additional side effects. Patients required 300-400 units of insulin a day, since only 10% of the inhaled insulin is bioavailable. Safety studies are in progress to determine whether long-term use affects pulmonary tissues.

E. Transplantation

Pancreas transplantation at the time of renal transplantation is becoming more widely accepted. Patients undergoing simultaneous pancreas and kidney transplantation have an 85% chance of pancreatic graft survival and a 92% chance of renal graft survival after 1 year. Solitary pancreatic transplantation in the absence of a need for renal transplantation should be considered only in those rare patients who fail all other insulin therapeutic approaches and who have frequent severe hypoglycemia or who have life-threatening complications related to their lack of metabolic control.

Islet cell transplantation is a minimally invasive procedure, and investigators in Edmonton, Canada, have reported initial insulin independence in a small number of patients with type 1 diabetes who underwent this procedure. Using islets from multiple donors and corticosteroid-free immunosuppression, percutaneous transhepatic portal vein transplantation of islets was achieved in over 20 subjects. Although all of the initial cohort was able to achieve insulin independence posttransplantation (some for more than 2 years of follow-up), a decline in insulin secretion has occurred over time and the subjects have again required supplemental insulin. All patients had complete correction of severe hypoglycemic reactions, leading to a marked improvement in overall quality of life. Even if long-term insulin independence is demonstrated, wide application of this procedure for the treatment of type 1 diabetes is limited by the dependence on multiple donors and the requirement for potent long-term immunotherapy.