What it is
Degarelix is a straight chain of ten amino acids — a decapeptide — closed at the end as an amide. The Firmagon label states that seven of the ten are unnatural amino acids and five are mirror-image D-forms. Natural GnRH is also ten residues long; degarelix keeps the length and rebuilds most of the chain:
- A bulky naphthylalanine, a chlorophenylalanine and a pyridylalanine at the front, all D-forms;
- Two modified aminophenylalanines in the middle, one carrying a hydroorotyl group, one a carbamoyl group;
- A lysine with an isopropyl tag, then proline, then D-alaninamide.
Its molecular weight is 1,632.3 Da.
How it works
The hypothalamus releases GnRH in pulses; the pituitary answers with LH and FSH; LH tells the testes to make testosterone. Prostate cancers usually depend on that testosterone.
There are two ways to cut the chain with a GnRH-like drug. An agonist such as leuprolide over-stimulates the receptor until it stops responding — so testosterone first rises, the "flare", then falls. A blocker such as degarelix binds the receptor reversibly and keeps GnRH off it, so testosterone falls from the start. The label states the mechanism in one line: it "binds reversibly to the pituitary GnRH receptors, thereby reducing the release of gonadotropins and consequently testosterone."
The trial against leuprolide
The label's trial (NCT00295750) randomised 620 men with prostate cancer to degarelix or leuprolide for a year, open-label, with a median age of about 73.
| Testosterone ≤ 50 ng/dL | Degarelix 240/80 mg (207) | Leuprolide 7.5 mg (201) |
|---|---|---|
| Day 1 | 52% | 0% |
| Day 3 | 96% | 0% |
| Day 7 | 99% | 1% |
| Day 14 | 99% | 18% |
| Day 28 | 100% | 100% |
| Days 28–364 (Kaplan–Meier) | 97.2% | 96.4% |
The trial's primary endpoint was testosterone suppression, not survival. PSA fell 64% at two weeks and 85% at one month on degarelix; the label adds that no evidence links the speed of PSA decline to clinical benefit.
A depot without a polymer
Like lanreotide, degarelix forms its own depot under the skin. The label reports a peak within about 2 days, a median terminal half-life of about 53 days — a consequence of very slow release — and breakdown by ordinary peptide hydrolysis, mostly cleared through bile into the faeces. It is not a substrate of the liver's CYP450 enzymes.
Safety
| Reaction (label trial, ≥ 5%) | Degarelix | Leuprolide |
|---|---|---|
| Injection-site reactions | 35% | < 1% |
| Hot flush | 26% | 21% |
| Raised liver enzymes (transaminases, GGT) | 10% | 5% |
| Weight gain | 9% | 12% |
| Hypertension | 6% | 4% |
The label's warnings are allergic reactions (including anaphylaxis), QT prolongation — QTcF ≥ 500 ms in fewer than 1% on degarelix and 2% on leuprolide — and harm to a fetus.
Where it stands
Drugs@FDA lists Firmagon (Ferring, NDA 022201, 2008-12-24) as a prescription product, and one generic application (Chia Tai Tianqing, ANDA 215791) with tentative approval dated 2025-08-18 (openFDA, 2026-10-05). It is injected under the skin of the abdomen by a healthcare provider; the schedule is set by the prescriber and followed by PSA. PubMed indexes 432 records, 52 tagged as randomised controlled trials (2026-10-05).
Related reading
Degarelix sits in this library's GnRH family beside the natural sequence, gonadorelin, the agonists leuprolide and triptorelin, and ganirelix, another blocker used for a different purpose: holding back ovulation during IVF.