Cosyntropin

Adrenocorticotropic hormone (ACTH) analog Diagnostic agent for adrenal function testing

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog IV or IM 5 mcg/kg (maximum 250 mcg per dog) Single dose Duration: One-time administration for ACTH stimulation test
Notes: For monitoring trilostane therapy, use 5 mcg/kg IV or IM; sample cortisol at 0 and 60 minutes (or 2 hours for trilostane).
Cat IV or IM 5 mcg/kg (maximum 125 mcg per cat) Single dose Duration: One-time administration for ACTH stimulation test
Notes: Sample cortisol at 0 and 60 minutes post-ACTH.
Horse IV or IM 100 mcg per horse (or 0.1 mg) Single dose Duration: One-time administration for ACTH stimulation test
Notes: For PPID diagnosis, sample cortisol at 0 and 60 minutes; some protocols use 0.1 mg IV.
Cattle IV or IM 0.25-1 mg per animal Single dose Duration: One-time administration
Notes: Limited data; use for research or specific diagnostic purposes.
Small Ruminants IV or IM 0.25 mg per animal Single dose Duration: One-time administration
Notes: Limited data; use for research or specific diagnostic purposes.
Rabbit IV or IM 5-10 mcg/kg Single dose Duration: One-time administration
Notes: Limited data; use for research or specific diagnostic purposes.

Clinical Indications & Species Uses

General Indications
  • Adrenal function testing in various species
Dog (Canine)
  • Diagnosis of hyperadrenocorticism (Cushing's syndrome)
  • Diagnosis of hypoadrenocorticism (Addison's disease)
  • Monitoring response to mitotane or trilostane therapy
Cat (Feline)
  • Diagnosis of hyperadrenocorticism
  • Diagnosis of hypoadrenocorticism
Horse (Equine)
  • Diagnosis of pituitary pars intermedia dysfunction (PPID, equine Cushing's disease)
  • Diagnosis of adrenal insufficiency
Cattle (Bovine)
  • Diagnosis of adrenal function in cases of suspected hypoadrenocorticism
Small Ruminants (Sheep / Goat)
  • Diagnosis of adrenal function (rarely used)
Rabbit & Small Mammals
  • Diagnosis of adrenal function (rarely used)

Pharmacology & Mechanism of Action

Drug Class: Adrenocorticotropic hormone (ACTH) analog | Pharmacological Group: Diagnostic agent for adrenal function testing

Mechanism of Action: Cosyntropin is a synthetic analog of adrenocorticotropic hormone (ACTH) consisting of the first 24 amino acids of the natural hormone. It binds to melanocortin-2 receptors (MC2R) on the adrenal cortex, activating adenylate cyclase and increasing intracellular cyclic AMP. This stimulates the adrenal cortex to synthesize and release glucocorticoids (primarily cortisol), and to a lesser extent mineralocorticoids and androgens. The diagnostic use relies on the adrenal gland's response to exogenous ACTH, which is blunted in adrenal insufficiency and exaggerated in hyperadrenocorticism.

Pharmacodynamics: After administration, cosyntropin produces a dose-dependent increase in plasma cortisol levels, peaking at 30-60 minutes after IV administration and 60-120 minutes after IM administration. In normal animals, cortisol levels rise to at least 2-3 times baseline. The response is used to assess adrenal function. In dogs with pituitary-dependent hyperadrenocorticism, the response is exaggerated; in adrenal insufficiency, the response is minimal or absent.

⚑ Pharmacokinetics Summary

Absorption: Cosyntropin is rapidly absorbed after IM or SC administration, with peak plasma levels achieved within 15-30 minutes.
Distribution: It distributes widely in the extracellular fluid. It does not cross the blood-brain barrier significantly.
Metabolism: Cosyntropin is rapidly metabolized by plasma and tissue peptidases, with a short half-life.
Excretion: Metabolites are excreted in the urine. The parent compound is not significantly excreted unchanged.
Half-Life: Plasma half-life is approximately 15 minutes in dogs and cats.
Bioavailability: IM and SC administration yields near-complete bioavailability.
Protein Binding: Minimal protein binding.

Available Formulations & Strengths

Injectable Solution (lyophilized powder for reconstitution) 0.25 mg/vial (250 mcg) (IV, IM, SC)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to cosyntropin or any component of the formulation
  • Do not use in animals with known adrenal hyperfunction (unless for diagnostic purposes under controlled conditions)
  • Do not use in animals with acute adrenal crisis (may worsen condition if not treated with glucocorticoids)
Warnings & Clinical Precautions:
  • For diagnostic use only; not intended for therapeutic use.
  • Use with caution in animals with cardiovascular disease, as transient hypertension may occur.
  • In animals with suspected hypoadrenocorticism, have emergency glucocorticoid therapy available.
  • Reconstituted solution should be used immediately; discard any unused portion.
  • Do not administer to pregnant animals unless benefits outweigh risks (limited safety data).
  • In horses with PPID, stress during testing may affect results; minimize handling.

Adverse Effects & Reactions

Common:

  • Transient injection site pain
  • Mild tachycardia
  • Hypotension or hypertension (rare)

Serious / Severe:

  • Anaphylactic reactions (rare)
  • Adrenal hemorrhage (very rare)
  • Electrolyte imbalances (if repeated doses)

Rare:

  • Allergic reactions
  • Seizures (in predisposed animals)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Corticosteroids (e.g., prednisone, dexamethasone) Exogenous corticosteroids suppress endogenous ACTH and adrenal response, leading to false-negative results. High
Mitotane Mitotane destroys adrenal cortex; response to cosyntropin may be reduced or absent. Moderate
Trilostane Trilostane inhibits cortisol synthesis; response to cosyntropin may be blunted. Moderate
Ketoconazole Ketoconazole inhibits adrenal steroidogenesis; may reduce cortisol response. Moderate
Phenobarbital May increase metabolism of cosyntropin, potentially reducing its effect. Mild

Overdose & Toxicity Management

Signs of Toxicity:

  • Excessive cortisol release leading to hypercortisolemia
  • Electrolyte imbalances (hypokalemia, hypernatremia)
  • Hypertension
  • Hyperglycemia
  • Immunosuppression (with prolonged exposure)

Emergency Treatment Protocol: Overdose is unlikely due to single diagnostic use. If overdose occurs, provide supportive care: monitor vital signs, correct electrolyte imbalances, and administer fluids. In severe cases, consider short-acting glucocorticoid antagonists (e.g., mifepristone) but not routinely recommended.

Food Animal Withdrawal Times

πŸ₯© Meat: 0 daysπŸ₯› Milk: 0 daysπŸ₯š Eggs: 0 days

Cosyntropin is a diagnostic agent with a very short half-life; no withdrawal periods are required for food animals. However, follow local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store lyophilized powder at 2-8Β°C (refrigerated). After reconstitution, use immediately; if necessary, store at 2-8Β°C for up to 24 hours.

Light Sensitivity: Light-sensitive β€” protect from direct exposure.

Handling & Special Conditions: Protect from light. Do not freeze.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for veterinary use in dogs and cats (e.g., Cortrosyn).

Extra-Label (Off-Label) Use: In the US, cosyntropin is FDA-approved for diagnostic use in dogs and cats. Extra-label use in other species is permitted under AMDUCA with appropriate veterinary oversight and withdrawal times.

Clinical Pearls & Practice Notes

πŸ’‘ Clinical Insights: Cosyntropin is the preferred agent for ACTH stimulation testing in veterinary medicine due to its reliability and safety. It is essential to follow standardized protocols for timing of blood samples. In dogs, the test is commonly used to diagnose hyperadrenocorticism and to monitor trilostane therapy. In horses, it is used to diagnose PPID. Always interpret results in light of the animal's clinical signs and other diagnostic tests. Ensure proper handling and rapid administration after reconstitution to maintain potency.

References & Literature

  • πŸ“š Plumb's Veterinary Drug Handbook
  • πŸ“š Papich Veterinary Pharmacology and Therapeutics
  • πŸ“š Compendium of Veterinary Products (CVP)