Primarily insulin is produced in freeze dried (lyophilized) powdered form and stored deepfrozen. It is then marketed in two forms: (1) sub-cutaneous injectable and (2) inhalable. Inject able insulin is a crystalline suspension of insulin crystals in a clear fluid.
Most of the companies manufacture insulin in the form of subcutaneous injections, which are again of following types: Humulin R, N, L U, 50/ 50, and 70 / 30.
Humulin R:
It is the regular insulin. It consists of zinc-insulin crystals dissolved in a clear fluid. It takes effect rapidly and has a short duration of activity (4-12 hours) as compared to other insulin.
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Humulin N:
It is a crystalline suspension of human insulin with protamine and zinc. It is intermediate-acting insulin with a slower rate of action and a longer duration of activity (up to 24 hours).
Humulin L:
It is an amorphous and crystalline suspension of human insulin with a slower onset and a longer duration of activity (up to 24 hours).
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Humulin U:
It is a crystalline suspension of human insulin with zinc providing a slower onset and a longer duration of activity (up to 28 hours).
Humulin R is referred to as fast acting, while N and L as intermediate were acting and U as slow acting.
Humulin 50 / 50: It is a mixture of 50% human insulin isophane suspension and 50% human insulin injection. It is intermediate-acting insulin with more rapid onset of action than regular insulin and duration of activity lasting up to 24 hours. Humulin 70 / 30: It is a mixture of 70 % of human insulin isophane suspension and 30 % human insulin injection. It is intermediate-acting insulin with a rapid onset of action and a longer duration of activity (up to 24 hours).
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Injectable humulin is available as pre-filled vials or disposable pre-filled pens. Sub-cutaneous injections are prepared until a vial contains an insulin suspension, while a disposable pen contains a sub-cutaneous needle with a precise quantity of insulin suspension.
The pen is disposed off after its use. It is not meant for re-use. Humulin R and 70/30 are available both as vials and pens while others are marketed as vials.
However, Pfizer and Inhale Corporation, USA manufacture inhalable insulin by a process called micronization, where very small particles are produced suitable for blister capsules to be used in a normal inhaler.