Pharmacotherapeutic group: Drugs used in diabetes. Insulins and analogues for injection, intermediate-acting, insulin (human). ATC code: A10AC01.
Pharmacology: Pharmacodynamics: The blood glucose lowering effect of insulin is due to the facilitated uptake of glucose following binding of insulin to receptors on muscle and fat cells and to the simultaneous inhibition of glucose output from the liver. Protaphane is a long-acting insulin.
Onset of action is within 1½ hours, reaches a maximum effect within 4-12 hours and the entire duration of action is approximately 24 hours.
Pharmacokinetics: Insulin in the blood stream has a half-life of a few minutes. Consequently, the time-action profile of an insulin preparation is determined solely by its absorption characteristics.
This process is influenced by several factors (e.g. insulin dosage, injection route and site, thickness of subcutaneous fat, type of diabetes). The pharmacokinetics of insulin products are therefore affected by significant intra- and inter-individual variation.
Absorption: The maximum plasma concentration of the insulin is reached within 2-18 hours after subcutaneous administration.
Distribution: No profound binding to plasma proteins, except circulating insulin antibodies (if present) has been observed.
Metabolism: Human insulin is reported to be degraded by insulin protease or insulin-degrading enzymes and possibly protein disulfide isomerase. A number of cleavage (hydrolysis) sites on the human insulin molecule have been proposed; none of the metabolites formed following the cleavage are active.
Elimination: The terminal half-life is determined by the rate of absorption from the subcutaneous tissue.
The terminal half-life (t½) is therefore a measure of the absorption rather than of the elimination per se of insulin from plasma (insulin in the blood stream has a t½ of a few minutes). Trials have indicated a t½ of about 5-10 hours.
Toxicology: Preclinical safety data: Non-clinical data reveal no special hazard for humans based on conventional studies of safety pharmacology, repeated dose toxicity, genotoxicity, carcinogenic potential, toxicity to reproduction.