Tetracosactide
Diagnostic agents
Diagnostic agents
Synthetic ACTH (its first 24 amino acids) used for the ACTH stimulation test: if cortisol does not rise, the adrenal glands are failing.
Also called: cosyntropin, ACTH 1-24, tetracosactrin
Quick facts
- Group
- Diagnostic agents
- Target
- Melanocortin-2 receptor (ACTH receptor) on adrenal cortex cells
- Key effects
- Rash · Fast or slow heart rate · Raised blood pressure
- Monitor
- Serum cortisol before
- ATC
- H01AA02
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows natural ACTH (its first residues) bound to MC2R with its partner protein MRAP1; tetracosactide is the first 24 amino acids of ACTH.
Tetracosactide is the first 24 amino acids of ACTH, the part that carries all of the hormone's adrenal-stimulating activity. It binds the ACTH receptor on adrenal cortex cells and makes them release cortisol within minutes. In the stimulation test, cortisol is measured before and after the injection: a healthy adrenal cortex responds with a clear rise, a failing one does not. Because the fragment is short, it is less allergenic than natural ACTH.
- Baseline cortisol is drawn
- Tetracosactide binds adrenal ACTH receptors
- A healthy adrenal cortex releases cortisol
- A low stimulated cortisol suggests adrenal insufficiency
Indications
- Diagnostic screening for adrenocortical insufficiency (ACTH stimulation test), in adults and children Adrenal insufficiency →
Adverse effects
Common
- Rash
- Fast or slow heart rate
- Raised blood pressure
- Peripheral oedema
Contraindications
- Previous hypersensitivity to tetracosactide or its excipients
Key interactions
- Glucocorticoids (for example hydrocortisone, prednisolone) and spironolactone
- Can falsely raise measured cortisol; usually withheld on the test day
- Oestrogen-containing medicines
- Raise cortisol-binding globulin and total cortisol; typically stopped weeks before testing
What is monitored
- Serum cortisol before and after the injection
- Signs of an allergic reaction during and after the test
- Conditions that alter cortisol-binding globulin (cirrhosis, nephrotic syndrome), which make results less reliable
Administration and safety
- The powder is reconstituted before injection
- Blood samples are timed exactly and labelled with the collection time
- Resuscitation equipment is ready in case of anaphylaxis
Pregnancy and breastfeeding
Decades of case reports have not shown an increase in birth defects or miscarriage; untreated adrenal insufficiency is itself dangerous in pregnancy.
Nursing care
- Check which steroid or oestrogen medicines the patient takes and whether they were withheld
- Draw the baseline sample before the injection
- Observe the patient for allergic reactions
- Do not delay treatment of suspected adrenal crisis to complete the test
Pharmacokinetics
- Absorption
- Given by intravenous or intramuscular injection
- Onset and duration
- Cortisol is measured about 30 and 60 minutes after the injection
Test yourself
Think of the answer, then tap the question to see it.
What is tetracosactide?
A synthetic peptide made of the first 24 amino acids of ACTH, which carry its full adrenal-stimulating activity.
What result of the ACTH stimulation test suggests adrenal insufficiency?
A low stimulated cortisol: the adrenal cortex does not respond with a clear rise.
Which medicines can falsely raise cortisol during the test?
Glucocorticoids and spironolactone; oestrogens raise total cortisol through cortisol-binding globulin.
Connections
← Back to the class: Diagnostic agents
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - COSYNTROPIN injection, powder, lyophilized, for solution (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Cryo-EM structure of ACTH-bound melanocortin-2 receptor in complex with MRAP1 and Gs protein (RCSB Protein Data Bank, 2026).
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Representative model, for educational purposes only.