Degarelix

Degarelix is a linear decapeptide amide containing seven unnatural amino acids, five of them D-isomers, engineered for high GnRH receptor affinity and minimal histamine release. On subcutaneous injection it self-assembles into a gel depot at the injection site, releasing drug over a month, which is why its apparent terminal half-life is around 53 days. Because it is an antagonist, testosterone falls to castrate levels in roughly 3 days rather than 3 to 4 weeks, and there is no flare - which matters enormously in men with spinal metastases or bladder outlet obstruction. It also suppresses FSH more completely than agonists do, and the phase 3 comparison against leuprolide showed a lower rate of PSA progression events.

Targets: GnRH receptor (GnRHR), Pituitary gonadotrophs, LH, FSH, Testosterone

• · Injected into the abdominal region, avoiding areas subject to pressure from a belt or waistband. Deep subcutaneous, not intramuscular or intravascular.
• · 80 mg in 4 mL at 20 mg/mL. Missing the 28-day window lets testosterone climb back, so scheduling discipline matters more than with 3- and 6-month agonist depots.

Work out your exact syringe units →

• very commonInjection-site reactions— Pain, erythema, swelling and induration in roughly 35 to 40 percent, mainly after the loading dose. This is degarelix's biggest tolerability disadvantage against leuprolide.
• very commonHot flushes
• commonWeight gain
• commonFatigue
• commonRaised transaminases— Usually transient and rarely clinically significant.
• commonBone mineral density loss— With long-term therapy, as with all androgen deprivation.
• uncommonQT prolongation— A class effect of androgen deprivation.
• rareHypersensitivity or anaphylaxis

• Known hypersensitivity to degarelix or any component.
• Pregnancy - it is not indicated in women and can cause fetal harm.
• Congenital long QT syndrome or uncorrected electrolyte abnormalities, relatively.

• cautionQT-prolonging drugs including class IA and III antiarrhythmics — Additive QT effect on top of androgen deprivation.
• redundantleuprolide — Same endpoint. Degarelix gets there faster and without a flare; leuprolide is more convenient and better tolerated at the injection site.
• conflictgonadorelin — Direct competitive receptor block.
• redundantAntiandrogens such as bicalutamide — Flare cover is unnecessary with an antagonist, which is much of the point of using one.

• · Testosterone at baseline and periodically - it should be under 50 ng/dL by day 3 and stay there.
• · PSA every 3 to 6 months.
• · Liver enzymes periodically.
• · ECG and electrolytes in men with cardiac risk or on other QT-prolonging drugs.
• · Bone density with long-term therapy.

Prescription drug in the US and EU for advanced hormone-sensitive prostate cancer.

• Firmagon (degarelix for injection) prescribing information (label)
• Klotz et al. 2008, phase 3 randomised trial of degarelix versus leuprolide in prostate cancer, BJU International (trial)
• Lopes et al. 2021, PRONOUNCE cardiovascular safety trial of degarelix versus leuprolide, Circulation (trial)

Degarelix is the answer to the single biggest problem with GnRH agonists in prostate cancer: the flare. Because it is a competitive antagonist with no intrinsic activity, there is no stored-gonadotropin release, no testosterone surge, and no window in which a man with spinal metastases can deteriorate from his own treatment. The registration data make the difference stark - 52 percent of men are at castrate testosterone by day 1 and 96 percent by day 3, against three to four weeks for an agonist. FSH suppression is also deeper than with agonists, because the receptor is blocked outright rather than downregulated with some residual signalling, and there is a body of opinion that this contributes to the PSA control seen early on. The clever part of the molecule is not the pharmacodynamics but the delivery. Degarelix contains p-ureido-phenylalanine residues that cause it to self-assemble into a gel depot at the subcutaneous injection site, releasing drug slowly enough to give a 53-day terminal half-life from an ordinary injection with no microsphere, no polymer and no implant. That is also why the injection produces such a high rate of local reactions - you are creating a deliberate deposit of drug under the skin, and the tissue responds to it. The maintenance schedule of 80 mg monthly after a 240 mg load exists because the depot needs re-establishing before the previous one is exhausted, and a late dose lets testosterone begin to escape.

Injection-site reactions are the dominant practical complaint and they are more than trivial - pain, erythema, swelling and induration are common with the loading dose in particular, because the drug deliberately forms a gel deposit under the skin. Most settle, but they recur with each monthly injection. Transaminase elevations occur and are worth checking rather than assuming. Late maintenance doses are the scheduling failure that matters: the depot is designed for 28-day replacement and testosterone begins to escape if the interval stretches. Beyond that, everything that goes wrong with androgen deprivation generally goes wrong here too - hot flushes, fatigue, bone loss, metabolic syndrome, mood change - because the antagonist mechanism spares you the flare, not the consequences of castration. And degarelix cannot be given as a three-monthly or six-monthly product, so it demands twelve injections a year against as few as two for some agonist depots, which is the main reason it has not displaced them entirely.

1. 240 mgDay 1 — The 240 mg loading dose, given as two 120 mg subcutaneous injections. This establishes the depot and is what produces castrate testosterone within three days.
2. 80 mgFrom day 28, monthly — 80 mg maintenance every 28 days. This is a genuine loading-then-maintenance schedule rather than a titration, and late maintenance doses allow testosterone to escape.

• GnRH receptor (GnRHR) on pituitary gonadotrophs — High-affinity competitive antagonism; a specific Kd was not resolved here.

  Immediate blockade with no agonist activity. Testosterone reaches castrate levels in 52 percent of men by day 1 and 96 percent by day 3, with no flare at any point.

• FSH

  Deeper and more sustained suppression than with agonists, since the receptor is blocked rather than desensitised with residual signalling.

• Extrapituitary GnRH receptors on prostate tumour cells

  A direct antagonist effect on tumour-expressed GnRH receptors has been proposed as contributing to outcomes independent of castration. Not established in humans.

• CS21 - degarelix versus leuprolide 12-month phase 3 study 3 · n=610 · 52 weeks · 2008

  Testosterone suppression to 50 ng/dL or below from day 28 through day 364. Degarelix achieved 97.2 percent overall castration rate, with 52 percent castrate by day 1 and 96 percent by day 3 - a speed no agonist can match - against 207 patients on degarelix 240/80 mg and 201 on leuprolide.

Testosterone falls immediately: 52 percent of men are castrate within 24 hours and 96 percent by day 3. There is no flare at any point. PSA begins falling within days. Hot flushes typically start in the first weeks as testosterone bottoms out, and arrive sooner than with an agonist for the obvious reason. The 240 mg loading depot covers the first 28 days, after which 80 mg monthly maintains it. The terminal half-life of about 53 days means the drug persists well beyond the last dose, so testosterone recovery after stopping takes months rather than weeks. Bone and metabolic consequences accumulate over years exactly as with the agonists.

The most important stacking fact about degarelix is a negative one: it needs no antiandrogen flare cover, because there is no flare. That removes weeks of bicalutamide and its own side effects from the start of therapy, and it is a genuine simplification rather than a marketing point. Bone protection with calcium, vitamin D and often a bisphosphonate or denosumab belongs in any long-term androgen deprivation plan regardless of which agent produces it. Watch other QT-prolonging drugs, since androgen deprivation lengthens QT on its own. There is essentially no cytochrome P450 interaction profile, which is unusually convenient in a population typically on several cardiovascular drugs. Combining with a GnRH agonist is contradictory. Gonadorelin and kisspeptin are inert against a blocked receptor.

Against leuprolide, triptorelin and goserelin, degarelix's advantage is speed and the absence of a flare, and it is decisive in exactly one situation - a man with high-volume metastatic disease at risk of cord compression or urinary obstruction, where an agonist flare can cause permanent harm. Its disadvantages are monthly injections against three-monthly or six-monthly agonist depots, and a substantially higher rate of injection-site reactions. There has been long-running debate about whether antagonists confer a cardiovascular advantage over agonists in men with pre-existing cardiovascular disease, and it remains genuinely unsettled rather than established. Against cetrorelix and ganirelix, degarelix is the same receptor logic built for months rather than days - a depot antagonist for oncology against short-acting antagonists for fertility cycles.

$400–$900/month. Firmagon in the US has commonly run several hundred to around a thousand dollars per monthly 80 mg maintenance dose, with the 240 mg loading dose costing more. Monthly administration means twelve clinic visits a year, which is a real cost on top of the drug. Figures are indicative and were not verified in this session.

• ?The full amino acid sequence with all unnatural residues was not verified from a primary source in this session.
• ?The volume of distribution is recorded as 1000 L because the label states only that it exceeds 1000 L, indicating distribution throughout total body water. The true value is not pinned down.
• ?Absolute bioavailability is not stated in the label and is not a well-defined parameter for a self-assembling depot.
• ?Cmax has a coefficient of variation of 83 percent, meaning exposure varies enormously between individuals from an identical dose. Any single pharmacokinetic figure here should be read as a population midpoint rather than a prediction.
• ?The time to steady state of 28 days is inferred from the loading-to-maintenance schedule rather than from a stated value.
• ?Whether GnRH antagonists reduce cardiovascular events compared with agonists remains unresolved in the literature, and I did not attempt to adjudicate it here.
• ?Cost figures are indicative and were not verified in this session.

• The efficacy and safety of degarelix: a 12-month, comparative, randomized, open-label, parallel-group phase III study in patients with prostate cancer Klotz L, Boccon-Gibod L, Shore ND, Andreou C, Persson BE, Cantor P, Jensen JK, Olesen TK, Schröder FH, BJU International, 2008 · PMID 19035858

  The pivotal head-to-head against leuprolide. The day 1 and day 3 castration figures are the entire clinical argument for antagonists in men who cannot afford a flare.

• FIRMAGON (degarelix) for injection - FDA prescribing information DailyMed / FDA

  Source of the 53-day terminal half-life, the greater than 1000 L volume of distribution, 90 percent protein binding, 9 L/h clearance, the 70 to 80 percent faecal elimination, and the day 1 and day 3 castration rates.