Diabetes Type I...Insulin Therapy (cont.)

For example, a patient may take an injection of Lente in the morning and evening to provide a baseline of insulin throughout a 24-hour period. In addition, the same patient may take an injection of Humalog just before meals to cover the increase in carbohydrate load after eating.

Not only is the variety of insulin preparations available growing, so are the methods for administering insulin. In the past, insulin was available only in an injectable form. This involved carrying syringes (which a few decades age were made of glass and required sterilization), needles, vials of insulin, and alcohol swabs. Needless to say, patients often found it difficult to take multiple shots a day, and as a result, good blood sugar control was often compromised. Many pharmaceutical companies are now offering discreet and convenient methods of insulin delivery. Novo Nordisk and Lily and Aventis have an insulin pen delivery system. This system is similar to an ink cartridge in a fountain pen. A small pen-sized device holds an insulin cartridge (usually containing 300 units). Cartridges are available in the most widely used insulin formulations, such as those listed in the table above. The amount of insulin to be injected is dialed in by turning the bottom of the pen until the required number of units is seen in the dose-viewing window. The tip of the pen consists of a needle that is replaced with each injection. A release mechanism allows the needle to penetrate just under the skin and deliver the required amount of insulin. The cartridges and needles are disposed of when finished, and new ones are simply inserted. These insulin delivery devices are discreet and less cumbersome than traditional methods.

Insulin Pump

The most recently available advance in insulin delivery is the insulin pump. In the United States, MiniMed and Disetronic and Deltronic market the insulin pump. An insulin pump is composed of a pump reservoir similar to that of an insulin cartridge, a battery-operated pump, and a computer chip that allows the user to control the exact amount of insulin being delivered. Currently, pumps on the market are about the size of a beeper. The pump is attached to a thin plastic tube (an infusion set) that has a soft cannula (or needle) at the end through which insulin passes. This cannula is inserted under the skin, usually on the abdomen. The cannula is changed every 3 days. The tubing can be disconnected from the pump while showering or swimming. The pump is used for continuous insulin delivery, 24 hours a day. The amount of insulin is programmed and is administered at a constant rate (basal rate).

Often, the amount of insulin needed over the course of 24 hours varies depending on factors like exercise, activity level, and sleep. The insulin pump allows for the user to program many different basal rates to allow for this variation in lifestyle. In addition, the user can program the pump to deliver a "bolus" during meals to cover the excess demands of carbohydrate ingestion. Over 50,000 people worldwide are using an insulin pump. This number is growing dramatically as these devices become smaller and more user friendly. Insulin pumps allow for tight blood sugar control and lifestyle flexibility while minimizing the effects of low blood sugar (hypoglycemia).

At present, the pump is the closest device on the market to an artificial pancreas. Naturally, the next step would be a pump that can also sense blood sugar levels and adjust the insulin delivery accordingly. At present, the newer pumps allow for communication with hand held meters through an infra red system, This allows the glucose reading from the finger stick to be transferred to the pump. The pump can then perform a calculation to determine if a bolus of insulin is needed, and if so, how much. The user can then use the advice at his/.her discretion. Ideally the next step is to take that blood glucose reading directly from a device connected to the pump avoiding the finger stick. Much effort is being concentrated on this area of research and possibly, even within the next year, a prototype device will be available for trial.

Inhalation

Another promising route of insulin administration is through inhalation. Inhaled insulin is currently being tested but has not been approved by the United States Food and Drug Administration (FDA). Many devices are available that allow for other medications to be used in this manner, the best example of which is asthma therapy. Insulin is not absorbed through the bronchial tubes (airways), and must reach the air sacks at the end of the bronchial tubes (alveoli) to be absorbed. Once at the alveoli, insulin can be absorbed and enter the bloodstream. Currently, powdered inhalers and nebulizers are being studied to determine which delivery system is the most reliable. The safety of inhaled insulin still needs to be established before a product for consumer use can be made available. One of the closest to market is Exubera, marketed by Pfizer.

Intranasal, Transdermal, Pill

Other routes for the delivery of insulin have also been tried. Intranasal insulin delivery was thought to be promising. However, this method was associated with poor absorption and nasal irritation. Transdermal insulin (skin patch delivery) has also yielded disappointing results to date. Insulin in pill form is also not yet effective since the digestive enzymes in the gut break it down.

The Future

Ultimately, the goal in the management of type 1 diabetes is to provide insulin therapy in a manner that mimics the natural pancreas. Perhaps the closest therapy available at this time is a transplant of the pancreas. Several approaches to pancreatic transplantation are currently being studied, including the whole pancreas and isolated islet cells (these groups of cells contain beta cells that are responsible for insulin production). Data available from 1995 indicates that almost 8,000 patients underwent pancreatic transplantation. Most patients undergo pancreatic transplantation at the time of kidney transplantation for diabetic kidney disease.