5.1. Current Delivery Options

The current preferred method of administering insulin is via subcutaneous injection. Multiple doses are required, up to three times daily. Different formulations are available, for example oily suspensions which have a depot effect, or formulations which consists of insulin complexed with protamine, which is a strongly basic protein from fish testes. In addition the insulin can be in either the crystalline or amorphous form, and this influences the rate of dissolution, and hence the rate of uptake. These many different formulations are necessary, because diabetics do not all respond equally to a given dose. Some diabetics have a very slow reaction time, and require a rather fast acting formulation, others react rapidly, requiring a slow acting formulation while others still are in between these two extremes.

The standard Insulin injection, a solution called USP standing for the United States Pharmacopoeia, has a rapid onset of activity of between one half and one hour, which peaks in two to three hours. After six hours the activity has subsided. Other forms with different activity are shown in Table 5.1.1. The amorphous form, or Semilente, has a similar onset to the USP, of 0.5 to one hour, but it peaks in 5-7 hours and lasts up to 16 hours and the Ultralenet form, which is the crystalline form has an onset of between 4 to 8 hours, a peak in 16 - 18 hours, and a duration of about a day, and finally the Lent form, which is a mixture of the two other forms, has an onset and duration between the amorphous and the crystalline form. With careful titration of the patient, is possible to limit the number of daily injections for the patient. Another long acting form is the complex with globulin from beef blood, and zinc. This form has a two hour onset peaks between 8 - 16 hours and lasts for about a day. The longest acting formulation is the protamine zinc suspension, which has a slow onset between 4 to 8 hour after injection, and a peak between 14 - 20 hours and a 36 hour duration. In the table, Normglycemic activity refers to the time at which insulin activity is evident.

Table 5.1.1. Timing of different insulin formulations

Normglycemic activity


Insulin Preparations

 

 

 

 

Onset

(hrs)

 

 

 

 

Peak

(hrs)

 

 

 

 

Duration

(hrs)


Insulin injection USP

 

0.5 - 1.0

 

2 - 3

 

6

Semilente

0.5 - 1.0

5 - 7

12 - 16

Lente

1.0 - 1.5

8 - 12

24

Ultralente

4 - 8

16 - 18

>36

Globin-Zn

~2

8 - 16

~24

Isophane suspension

1 - 1.5

8 - 12

~24

Protamine suspension

4 - 8

14 - 20

~36