About Insulin

About Insulin

ABOUT INSULIN

What is this stuff I have to take? Is
it a drug? Will it make me better, so I don't have to take it anymore? What
does it do? Why can't I just drink it, or take a big shot once a month? And
why are there so many different types? Will there ever be something better?

Insulin is a hormone, normally produced in

sufficient amounts by the healthy human pancreas. Its role is to facilitate the final

digestion of glucose by the human body. When insulin is lacking (diabetes), glucose

remains undigested in the blood. The body isn't being fed, and the high blood sugar can

cause damage, the ramifications of diabetes.

The two major types of diabetes (type 1 and type

2, IDDM and NIDDM) are separated by presence of insulin. The pancreas of the type 1

diabetic has ceased producing insulin, and insulin must be injected. This injected insulin

is a replacement, and, barring the transplantation of a healthy pancreas, will need to be

continued for life.

The type 2 (NIDDM) diabetic has an impaired

insulin supply. He or she doesn't have enough, or has some difficulty assimilating it

(insulin resistance), or both. Lifestyle and diet changes, and oral medications, some of

which stimulate the failing pancreas to produce more insulin, are used in treatment. Many

veteran type 2 diabetics find their insulin supply, already impaired, has lessened to the

point where they need to inject insulin.

Insulin cannot be taken by mouth because it is

digestible. Oral insulin would be obliterated in the stomach, long before it reached the

bloodstream where it is needed. Once injected, it starts to work and is used up in a

matter of hours. Depending on a number of factors, individuals vary insulin volume, type,

and frequency, to optimize blood glucose management.

That there are so many different formulations of

insulin is partly intentional, and partly an accident of history. Before insulin,

diabetics just died. When the hormone became available in the 1920s, doctors realized

patients' needs differed. As newer formulations of insulin became available, it was

discovered that the best blood sugar control was achieved by use of a mix of insulins of

different duration and time of onset (as described below). The earliest insulins were made

from animals ("animal source") but newer types are made "in the test

tube" ("recombinant DNA origin"). The existence of so many different

insulins helps the doctor tailor a dosage best for a specific individual. As new types of

insulin are invented, they will help achieve an even better "fit."

Many patients have specific questions about

insulin use. Some of the most common are listed below:

Q: How long before a meal should insulin be

injected?

A: With "Regular" insulin, it is

recommended you inject 30 minutes before meals. With Humalog (Eli Lilly & Co.'s trade

name for quick-acting Lispro insulin analog), a 10-minute wait is sufficient. Insulin

works far better when given sufficient time to do its job. Diabetes self-management

requires keeping to the established schedule. Too much time, or too little, will cause

problems. If you wait after injection for your blood glucose to drop, before you start to

eat, you may limit the "glycemic excursion" (blood sugar rise) that follows a

meal, but you are taking chances with possible hypoglycemia.

Q: Do insulin absorption rates vary from one

person to another?

A: Yes. Some diabetics get 16-20 hours out of an

NPH/Lente shot, while others get 8-12 hours. An individual can experience day to day

variation of up to 50%, with the same dose. The same person, with the same dose and

technique, may also see a day to day variation of 25-50% in time of insulin peak action.

Q: Does exercise affect absorption?

A: Yes. Exercise of a given muscle area after

injection of insulin into that area will cause the insulin to be absorbed faster. Exercise

in general burns up blood glucose, lessening the need for insulin to digest it, thus

increasing the effect of injected insulin. Massage of the injection site after injection

can help speed absorption.

Q: Which injection technique makes the insulin

work faster—Subcutaneous or Intramuscular?

A: Intramuscular (IM) injection is faster.

However, IM injection is not for regular use, and has its risks. Your doctor may use it in

special situations, but day to day insulin injections should all be of the subcutaneous

(SubQ) type. Mixing the two would inject another variable into your diabetes control.

Q: Does being a smoker change insulin absorption?

A: Yes. Along with all the other damage it does,

smoking decreases insulin absorption.

Q: What are the absorption differences between

insulin injection sites?

A: The abdomen is the fastest, followed by arms

and thighs (no data available on absorption rate in the buttocks). These differences may

be used to prolong or speed up the effect of insulin for special circumstances, but it is

best to keep injecting within one anatomical area, for consistency in time of onset.

Q: Does the speed with which I push the plunger

of the syringe make any difference?

A: No, velocity does not make any difference.

Q: Does the angle of injection make any

difference in absorption?

A: The angle of injection (45 to 90 degrees)

makes no difference.

Q: Does skinfold thickness affect absorption?

A: The more fat present in the injection site,

the slower the absorption.

Q: I want to switch from animal-source to human

insulin. Is there much difference?

A: Human (recombinant DNA) insulins work faster

than animal-source insulins of the same type, so you may need to recompute your daily

doses. Talk to your doctor.

Q: Why is "rolling" the insulin vial

before drawing up a shot preferable to shaking it?

A: The recommendation is to roll only the

suspension insulins, NPH and Lente. There is no need to agitate Regular insulin. Shaking

instead of rolling the vial would produce air bubbles.

Q: How should insulin be stored?

A: Insulin vials should be kept refrigerated

until you are ready to start using them. Then they need to be kept in a cool place, away

from extremes of temperature. Insulin is fragile, and exposure to extreme heat, or

freezing, can destroy its efficacy.

Q: How can I have a more flexible insulin

regimen?

A: Some people use sliding scales and algorithms

for the regular dose, according to the amount of food taken at the time. Use of such a

technique requires thorough familiarity.

Q: What is "buffered" insulin?

A: Buffered Regular insulin is for use in insulin

pumps. It acts just like other "R" insulins, but contains a buffering agent to

make it more stable for such use. Some folks use conventional, unbuffered, Regular in

their pumps, but the manufacturers recommend use of the buffered variety.

Q: What are the durations and peak times for the

different insulin classes?

LOWS MOST INSULIN START PEAK END LIKELY
AT

Lispro 10 min 1 hr 4 hr 2-4 hr

Regular 20 min 3-4 hr 8 hr 3-7 hr

NPH 1.5 hr 4-10 hr 22 hr 6-13 hr

Lente 2.5 hr 6-12 hr 24 hr 7-14 hr

Ultralente 4 hr 10-18 hr 36 hr 10-22 hr

(This chart is from "Stop the

Rollercoaster," by Walsh and Roberts, with further data provided by Eli Lilly &

Co. Please Note: Times are approximate, and will vary between individuals!)

Much of the above data were compiled by Arturo

Rolla, MD, of Harvard University School of Medicine.