Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2019 Publisher: Atnahs Pharma UK Ltd., Sovereign House, Miles Gray Road, Basildon, Essex, SS14 3FR, UK
Pharmacotherapeutic group: anterior pituitary lobe hormones and analogues – ACTH
ATC code: H01AA02
Tetracosactide acetate consists of the first 24 amino acids occurring in the ACTH sequence and displays the same physiological properties as ACTH. In the adrenal cortex, it stimulates the biosynthesis of glucocorticoids, mineralocorticoids, and, to a lesser extent androgens. Prolonged use of Synacthen is reported to have minimal suppression of hypothalamic-pituitary-adrenal axis as compared to long-term corticosteroids.
The site of action of ACTH is the plasma membrane of the adrenocortical cells, where it binds to a specific receptor. The hormone-receptor complex activates adenylate cyclase, stimulating the production of cyclic AMP (adenosine monophosphate) and so promoting the synthesis of pregnenolone from cholesterol. From pregnenolone the various corticosteroids are produced via different enzymatic pathways.
Tetracosactide is rapidly distributed and concentrated in the adrenals and kidneys, which lead to rapid decrease in its plasma levels.
There is no evidence of binding of ACTH to any particular plasma protein, though some non-specific interaction with albumin has been reported. Tetracosactide acetate has an apparent volume of distribution of approximately 0.4L/kg.
In the serum, tetracosactide acetate is broken down by serum endopeptidases into inactive oligopeptides and then by aminopeptidases into free amino acids. The rapid elimination from plasma is probably not attributable to this relatively slow cleavage process, but rather to the rapid concentration of the active substance in the adrenal glands and kidneys.
Following an intravenous injection, elimination of tetracosactide acetate from the plasma consists of 3 phases. The half-lives of these phases are approximately 7 minutes (0 to 1 hour), 37 minutes (1 to 2 hours) and 3 hours thereafter.
Following an iv dose of 131I-labelled tetracosactide acetate, 95 to 100% of the radioactivity is excreted in the urine within 24 hours.
No studies have been performed to evaluate the mutagenic or carcinogenic potential of tetracosactide. No animal studies on fertility and reproduction toxicity have been performed with tetracosactide.
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