1 What is this medicine
and what is it used for?
Tetracosactide (Synacthen) is a synthetic analogue of the
first 24 amino acids of natural ACTH (adrenocorticotrophic hormone) — the
pituitary hormone that stimulates the adrenal cortex to produce cortisol and
other corticosteroids. Synacthen 250 mcg injection is used predominantly as a
diagnostic agent.
Primary use — Short Synacthen Test (SST): A single 250 mcg
injection (IM or IV) is given, and serum cortisol is measured at 30 and/or 60
minutes. A cortisol rise to >500 nmol/L (or >550 nmol/L depending on
local assay) excludes primary adrenal insufficiency (Addison's disease). This
is the gold-standard functional test for adrenal reserve.
Secondary uses (therapeutic): Synacthen Depot (1 mg/mL
sustained-release) is used therapeutically in conditions such as multiple
sclerosis relapse, inflammatory bowel disease, and other
corticosteroid-responsive conditions — this is distinct from the 250 mcg
diagnostic formulation.
2 How this medicine is
given (diagnostic SST)
The Short Synacthen Test is performed in a clinic or hospital
setting by trained healthcare professionals. A baseline blood sample is taken
(0 minutes). Then 250 mcg of tetracosactide is given by IM injection (deltoid
or thigh) or IV injection. Further blood samples are collected at 30 minutes
and/or 60 minutes. All samples are sent to the laboratory for cortisol
measurement.
|
The test ideally takes
place in the morning (peak cortisol) — usually between 8 AM and 10 AM. No special fasting is
required for the SST, though some centres request no corticosteroid medicines
on the day of testing. Results are usually
available within 24–48 hours and interpreted by the requesting
endocrinologist. |
3 Possible side effects
|
Frequency |
Side Effect |
What to Do |
|
Uncommon (0.1–1%) |
Hypersensitivity
reactions (skin flushing, urticaria, itching) |
Usually mild and
transient. Healthcare team should monitor for 30 minutes after injection. |
|
Rare (<0.1%) |
Anaphylaxis |
Resuscitation
facilities must be available. Treat with adrenaline, antihistamine,
corticosteroids. |
|
Uncommon |
Transient blood
pressure changes |
Monitor BP for 30
minutes post-injection. |
|
With repeated
therapeutic use (Depot formulation) |
Corticosteroid-related
effects (fluid retention, hypertension, immunosuppression) |
Relevant for Synacthen
Depot therapeutic use, not single-dose diagnostic testing. |
4 Contraindications and
precautions
|
Contraindications / Cautions: Known hypersensitivity to tetracosactide or
corticotrophin — DO NOT administer; risk of anaphylaxis. Cushing's syndrome — adrenal cortex already
maximally stimulated; SST is not valid. Active infectious or inflammatory conditions —
proceed with clinical caution. Allergy history: ask specifically about latex
and other drug allergies before administration. Pregnancy: tetracosactide is not recommended in
pregnancy unless clearly necessary. |
5 Drug interactions
(diagnostic use)
For single-dose diagnostic use (SST), clinically significant
drug interactions are minimal. However:
• Exogenous corticosteroids taken on or
before the test day may cause a falsely elevated baseline cortisol and blunt
the response — some centres ask patients to omit morning corticosteroids on
test day.
• Oestrogens (oral contraceptive pill,
HRT): increase cortisol-binding globulin — may give falsely elevated total
cortisol results; free cortisol assays or Synacthen-stimulated salivary
cortisol testing may be preferred.
6 Storage
Store at 2–8°C (refrigerate). Do not freeze. Keep in original
carton to protect from light. Synacthen is for single use only — discard any
unused portion of the ampoule. Do not use if discoloured or if particles are
visible.
7 Prescription
requirement
|
PRESCRIPTION ONLY
MEDICINE (POM) — Prescribed and administered by an endocrinologist or
physician. Administration must be
by trained healthcare professional with anaphylaxis equipment available. |
8 Guidance for patients
undergoing the Short Synacthen Test
The Short Synacthen Test is a straightforward and safe test
to check how well your adrenal glands are working. It involves a single
injection followed by two blood tests over one hour — most patients experience
no side effects at all.
If your result shows your adrenal glands are not responding
adequately, this means you have adrenal insufficiency, and your doctor will
discuss treatment with cortisol replacement (hydrocortisone tablets). This is a
manageable, treatable condition once diagnosed.
If you have ever had a serious allergic reaction to a
steroid-type injection or hormonal injection in the past, tell your doctor
before the test.
9 Pharmacist &
prescriber notes
Synacthen 250 mcg/mL is the standard Short Synacthen Test
(SST) preparation — also known as the high-dose Synacthen test. A low-dose
Synacthen test (1 mcg) is used in some centres for greater sensitivity in
detecting subtle secondary/tertiary adrenal insufficiency, but requires
dilution of the standard 250 mcg ampoule.
The standard SST: 250 mcg IM/IV, cortisol at 0, 30, 60
minutes. Normal response: peak cortisol > 500 nmol/L (laboratory-dependent —
confirm local reference range). The SST does not distinguish primary from
secondary adrenal insufficiency in all cases — an ACTH level or further dynamic
testing (insulin tolerance test) may be required. Therapeutic Synacthen Depot
(1 mg/mL) is a separate product with a different formulation and different
indications.
10 Frequently asked
questions
What happens if my result is abnormal?
An abnormal result suggests your
adrenal glands are not producing enough cortisol on demand. Your
endocrinologist will arrange further tests to determine the cause and will
discuss treatment options, which usually involve taking a cortisol replacement
tablet (hydrocortisone) daily.
How should I prepare for the test?
Most centres ask you to come in the
morning (8–10 AM). You can eat and drink normally unless your doctor specifies
otherwise. If you take steroid medicines, ask your doctor whether to take your
usual dose on the morning of the test.
Can I drive after the test?
Yes — a single diagnostic SST does
not impair driving ability. You should feel completely normal after the test.
Are there any restrictions after the test?
No — you can resume normal activities
immediately after the blood draws are completed.