Cosyntropin
Tetracosactide
Also known as: Cortrosyn · Synacthen · Nuvacthen Depot · Cortrosina · tetracosactide · alpha(1-24)corticotrophin · beta(1-24)-corticotrophin · tetracosactido · tetracosactidum · tetracosactrin · tetracosapeptide · Cosyntropin
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Tentative diagnosis of Addison's disease | 0.25 mg (250 micrograms) of cosyntropin IV or IM | IV/IM | Once | — | 🌎 NA |
| ACTH Stimulation test | 1 microgram/kg or 250 micrograms/dog IV or IM | IV/IM | Once | — | 🌎 NA |
| Low dose ACTH stimulation test | 0.5 micrograms/kg IV | IV | Once | — | 🌎 NA |
| ACTH stimulation test | 5 μg/kg | IV/IM | once | single dose | 🌍 EU |
- Tentative diagnosis of Addison's disease: Draw baseline cortisol, give dexamethasone SP 2-5 mg/kg, give cosyntropin, draw second sample 45-60 mins later.
- ACTH Stimulation test: Measure serum cortisol before and 1 hour post injection.
- Low dose ACTH stimulation test: Peak concentrations at 60 minutes after dose.
- ACTH stimulation test: The same doses may be used for the lyophilized product but must be administered IM.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Tentative diagnosis of Addison's disease | 0.125 mg of cosyntropin IV or IM | IV/IM | Once | — | 🌎 NA |
| ACTH Stimulation test | 0.125 mg (total dose-125 mcg) IM or IV | IM/IV | Once | — | 🌎 NA |
| Diagnosis of hyperadrenocorticism | 125 micrograms/cat IM or IV | IM/IV | Once | — | 🌎 NA |
| Low dose ACTH stimulation test | 5 micrograms/kg | IV/IM | Once | — | 🌎 NA |
| ACTH stimulation test | 5 μg/kg or 125 μg/cat | IV/IM | once | single dose | 🌍 EU |
- Tentative diagnosis of Addison's disease: Draw baseline cortisol, give dexamethasone SP 2-5 mg/kg, give cosyntropin, draw second sample 45-60 mins later.
- ACTH Stimulation test: Begin test between 8-9 AM; obtain preinjection cortisol level and 30 minutes and 1 hour post.
- Diagnosis of hyperadrenocorticism: Cortisol measurements before and at 30 and 60 minutes post.
- Low dose ACTH stimulation test: Cortisol concentrations peak at 60 minutes post-dose.
- ACTH stimulation test: Cortisol response is less dramatic than in dogs; use feline-specific reference ranges.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Relative adrenal insufficiency (RIA) evaluation in critically ill horses | 0.1 micrograms/kg | IV/IM | Once | — | 🌎 NA |
| ACTH Stimulation test | 1 mg IV | IV | Once | — | 🌎 NA |
| ACTH Stimulation test (Foals) | 0.5 micrograms/kg IV | IV | Once | — | 🌎 NA |
- Relative adrenal insufficiency (RIA) evaluation in critically ill horses: Cortisol will peak after 30 minutes.
- ACTH Stimulation test: Administer between 8 and 10 AM; take post ACTH cortisol levels at 2 hours post dose.
- ACTH Stimulation test (Foals): Peak cortisol levels occur at 30 minutes post dose.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Cosyntropin is a synthetic polypeptide that mimics the effects of endogenous corticotropin (ACTH). It is primarily used as a diagnostic agent in veterinary medicine.
- Primary Use: Alternative to ACTH gel for adrenal function tests, specifically the ACTH stimulation test.
- Indications: Used to diagnose hypoadrenocorticism (Addison's disease), iatrogenic hyperadrenocorticism (Cushing's syndrome), and to monitor the response to mitotane or trilostane therapy.
- Clinical Pearl: It is less often recommended as a screening test for naturally occurring Cushing's syndrome in dogs due to relatively low sensitivity compared to the low-dose dexamethasone suppression test (LDDST).
- Advantage: Because it lacks the C-terminal portion of endogenous corticotropin, it is significantly less immunogenic, making it safer for patients who have previously reacted to ACTH of animal origin.
Mechanism of action
Cosyntropin acts identically to endogenous ACTH. It binds to melanocortin type 2 receptors (MC2R) in the adrenal cortex → stimulates the production of intracellular cAMP → promotes the conversion of cholesterol to pregnenolone → rapidly stimulates the adrenal cortex to secrete cortisol, corticosterone, and weak androgens.
Because it only contains the first 24 amino acids of natural corticotropin (which has 39), it retains full biological activity but lacks the highly immunogenic C-terminal amino acids (25-39).
Safety & warnings
Contraindications
- Known hypersensitivity to cosyntropin
- No information available
Adverse effects
- Hypersensitivity reactions (rare, but possible)
- Pain on intramuscular (IM) injection
Precautions
Hypersensitivity Warning: Use with caution in patients who have shown hypersensitive reactions to ACTH in the past, as cross-reactivity is a distinct possibility.
- Laboratory Interference: High bilirubin or free plasma hemoglobin can cause falsely high cortisol values in some assays.
Drug interactions
Cross-reacts with cortisol assays; patients should not receive these on test day (dexamethasone does not interfere).
May cause falsely high cortisol values if using a fluorometric analysis.
Monitoring
- Plasma or serum cortisol levels (baseline and post-stimulation)
- Patient monitoring for rare hypersensitivity reactions during the test
- Serum cortisol levels (baseline/pre-ACTH and post-ACTH, typically at 1 hour post-injection)
Pharmacokinetics
Half-life
Absorption
Rapidly absorbed after being given IM. Plasma cortisol levels reach their peak within an hour after IM or rapid IV administration.
Distribution
Rapidly distributed to the adrenal glands.
Metabolism
Inactivated by gut enzymes if given orally. It is unknown exactly how cosyntropin is inactivated or eliminated systemically.
Elimination
Unknown.
Overdose
Unlikely to be of clinical consequence if used one-time only for diagnostic purposes.
Available products
Formulations
- Solution for Injection
- 0.25 mg/ml injectable solution
- 0.1 mg/ml injectable solution
- 0.25 mg/ml lyophilized powder for injection
Human-labeled
- Cosyntropin Powder for Injection: 0.25 mg lyophilized (250 mcg) in single-dose vials with diluent; Cortrosyn (Amphastar)
- Cosyntropin Solution for Injection: 0.25 mg/mL, preservative free in 1 mL single-dose vials; generic (Sandoz)
- Synacthen 0.25 mg/ml solution for injection
Regulatory status
Human product often used under the cascade.
POM, Special. Human product used under the cascade.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
After reconstituting with sterile normal saline, the solution is stable for 24 hours at room temperature; 21 days if refrigerated. Do not add the drug to blood or plasma infusions. Reconstituted cosyntropin can be stored frozen (-20°C) in plastic syringes for up to 6 months and retain biologic activity in dogs. It is recommended to freeze in small aliquots to avoid repeated thawing and refreezing.
Client information
Diagnostic Use Only: This medication is used exclusively in the veterinary clinic to test how well your pet's adrenal glands are functioning.
- Procedure: Your pet will have a small blood sample drawn, receive an injection of this medication, and then have another blood sample drawn 30 to 60 minutes later.
- Preparation: Let your veterinarian know about any medications your pet is taking, especially steroids (like hydrocortisone or prednisone) or spironolactone, as these can interfere with the test results.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.