Stable premixed insulins (70% NPH and 30% regular) are available as a convenience to patients who have difficulty mixing insulin because of visual problems or insufficient manual dexterity. Premixed preparations of rapidly acting insulin analogs (lispro, aspart) and NPH are not stable because of exchange of the rapidly acting insulin analog for the human regular insulin in the protamine complex. Consequently, over time, the soluble component becomes a mixture of regular and rapidly acting insulin analog at varying ratios. To remedy this problem, intermediate insulins composed of isophane complexes of protamine with the rapidly acting insulin analogs were developed (neutral protamine lispro [NPL]; aspart protamine). Premixed combinations of NPL and insulin lispro are now available for clinical use (Humalog Mix 75/25 and Humalog Mix 50/50). These mixtures have a more rapid onset of glucose-lowering activity compared with 70% NPH/30% regular human insulin mixture and can be given within 15 minutes before or after starting a meal. A similar 70% insulin aspart protamine/30% insulin aspart (NovoLog Mix 70/30) is now available. The main advantages of these new mixtures are that (1) they can be given within 15 minutes of starting a meal and (2) they are superior in controlling the postprandial glucose rise after a carbohydrate-rich meal.
Insulin glargine or insulin detemir cannot be acutely mixed with either regular insulin or the rapid-acting insulin analogs. Insulin degludec, however, can be mixed and is available as 70% insulin degludec/30% insulin aspart and is injected once or twice a day.
A. Insulin Syringes and Needles
Disposable plastic syringes with needles attached are available in 1-mL (100 units), 0.5-mL (50 units), and 0.3-mL (30 units) sizes. The “low-dose” 0.3-mL syringes are popular because many patients with diabetes do not take more than 30 units of insulin in a single injection except in rare instances of extreme insulin resistance. They are also available in half-unit marking. Three lengths of needles are available; longer needles are preferable in obese patients to reduce variability of insulin absorption. If the skin is clean it is not necessary to use alcohol. Rotation of sites is recommended to avoid problems with absorption due to lipohypertrophy from overuse of injection sites.
B. Insulin Pens
The pens eliminate the need for carrying insulin vials and syringes. Cartridges of insulin lispro, insulin aspart, and insulin glargine are available for reusable pens (Lilly, Novo Nordisk, and Owen Mumford). Disposable prefilled pens are also available for regular insulin (U100, U500), insulin lispro, insulin aspart, insulin glulisine, insulin detemir, insulin glargine, insulin degludec, NPH, 70% NPH/30% regular, 75% NPL/25% insulin lispro, 50% NPL/50% insulin lispro, 70% insulin aspart protamine/30% insulin aspart, and 70% insulin degludec/30% insulin aspart (Table 41–6).
C. Continuous Subcutaneous Insulin Infusion Devices (CSII, Insulin Pumps)
Continuous subcutaneous insulin infusion devices are external open-loop pumps for insulin delivery. The devices have a user-programmable pump that delivers individualized basal and bolus insulin replacement doses based on blood glucose self-monitoring results.