Goserelin

Goserelin substitutes D-serine tert-butyl ether at position 6 and replaces the C-terminal glycinamide with azaglycine amide, making it both far more potent and far more protease-resistant than native GnRH. It is formulated in a polyglactin matrix rod that degrades steadily, delivering drug over 28 days or 12 weeks. As with all agonists in this class, the sequence is flare then downregulation, reaching castrate testosterone in men by about day 21. Its main indications are prostate and breast cancer, endometriosis and endometrial thinning before ablation, and it is also used for ovarian protection during chemotherapy.

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

• · 3.6 mg implant. Used in prostate cancer, breast cancer, endometriosis and pre-ablation endometrial thinning.
• · 10.8 mg implant, used primarily in prostate cancer.

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• very commonHot flushes and sweats
• very commonLibido loss
• commonInjection-site bruising or pain— The needle is wide - 14 to 16 gauge - and insertion genuinely hurts more than a normal injection.
• commonVaginal dryness and atrophy— In women.
• commonBone mineral density loss— The reason endometriosis courses are limited to 6 months unless add-back hormone therapy is used.
• commonMood disturbance
• commonHormone flare with symptom worsening— First 1 to 2 weeks.
• rareInjection-site vascular injury— The label carries a warning about inferior epigastric artery injury during insertion, particularly in thin or anticoagulated patients.

• Pregnancy and breastfeeding.
• Undiagnosed abnormal vaginal bleeding.
• Known hypersensitivity to GnRH analogues.
• Caution with anticoagulation because of the implant needle calibre and reported abdominal vascular injuries.

• cautionAnticoagulants — Raises the risk of haematoma or vascular injury at the abdominal implant site.
• synergyAntiandrogens such as bicalutamide — Combined androgen blockade and flare cover.
• conflictgonadorelin — Desensitises the receptor gonadorelin acts on.
• synergyAdd-back tibolone or low-dose oestrogen plus progestogen — Standard bone-protection strategy in long endometriosis courses.

• · Testosterone or oestradiol to confirm suppression.
• · PSA in prostate cancer.
• · DEXA bone density with courses beyond 6 months.
• · Injection-site inspection at each implant change.

Prescription drug worldwide.

• Zoladex (goserelin acetate implant) prescribing information (label)
• Moore et al. 2015, goserelin for ovarian protection during breast cancer chemotherapy (POEMS/S0230), New England Journal of Medicine (trial)

The receptor pharmacology is the shared class story - initial gonadotropin release, then uncoupling and downregulation under continuous exposure, castrate hormone levels at roughly 21 days. What distinguishes goserelin is entirely the delivery system, and it is worth understanding because it changes the risk profile rather than the effect. The drug is a solid rod of polyglactin, the same lactide-glycolide polymer used in absorbable surgical sutures, loaded with goserelin and pushed into the anterior abdominal wall through a 14 to 16 gauge needle. The polymer hydrolyses steadily and releases drug over 28 days or 12 weeks. Two consequences follow. First, the release profile is smoother than a microsphere suspension, with a less pronounced early burst. Second, the insertion itself is a minor procedure with real vascular risk - the label carries a specific warning about injury to the inferior epigastric artery, which is not a theoretical concern in thin or anticoagulated patients and has caused significant abdominal haemorrhage. The other pharmacological point worth flagging is the sex difference in clearance: women clear goserelin about 50 percent faster than men, and women also reach peak concentration over a wider window. Neither changes the dosing schedule, but it is a reminder that the same implant behaves measurably differently in different people. Goserelin's oncological range is broader than most in this class - prostate cancer, premenopausal breast cancer, endometriosis, endometrial thinning before ablation, and ovarian protection during chemotherapy, the last of which has randomised evidence behind it.

The insertion is the part that goes wrong in a way unique to this drug. It is a wide needle into the anterior abdominal wall, it hurts considerably more than a normal injection, and the label documents injury to the inferior epigastric artery with significant bleeding, particularly in thin or anticoagulated patients. Bruising and haematoma at the site are common and unremarkable; sudden severe abdominal pain after insertion is not, and needs assessing rather than tolerating. Beyond the procedure, the failures are the class failures: an initial flare with symptom worsening in the first fortnight, hot flushes and vaginal atrophy or erectile dysfunction as hormone levels fall, and bone loss that is the reason benign-indication courses are time-limited. In endometriosis specifically, the mistake is running repeated six-month courses without add-back and without a DEXA, on the reasoning that each individual course is within label.

• GnRH receptor (GnRHR) on pituitary gonadotrophs — Substantially more potent than native GnRH; a specific Kd was not resolved here.

  Flare then downregulation, producing castrate testosterone in men and postmenopausal oestradiol in women by around day 21.

• Ovarian follicular reserve (indirect)

  Suppressing the axis during chemotherapy appears to protect ovarian function, which is the basis of the POEMS trial result and a use quite unlike the rest of this class.

• Endometrial tissue (indirect, via oestradiol withdrawal)

  Endometrial atrophy, which is why goserelin is used to thin the endometrium before ablation and to treat endometriosis.

• POEMS / S0230 3 · 2015

  Rate of ovarian failure at two years in premenopausal women receiving cyclophosphamide-containing chemotherapy for hormone-receptor-negative breast cancer, with or without goserelin. Goserelin reduced ovarian failure and improved subsequent pregnancy rates - a use of androgen and oestrogen deprivation that protects rather than removes function.

Hormone flare occupies the first one to two weeks. Castrate testosterone or postmenopausal oestradiol arrives at around 21 days, and the label puts full suppression at two to four weeks. Hot flushes begin as levels fall. Amenorrhoea in women typically follows within the first one to two months. The implant's drug delivery runs for 28 days or 12 weeks depending on the product, and the next implant goes in at that interval regardless of how the patient feels. After the last implant, ovarian or testicular function typically returns over several months, and in the POEMS setting that recovery is the entire point.

Antiandrogen flare cover with bicalutamide is standard practice at the start of therapy in men with metastatic prostate cancer, exactly as with the other agonists. Add-back therapy with tibolone or low-dose oestrogen plus a progestogen is the established strategy for extending endometriosis courses beyond six months without losing bone, and it is well enough evidenced that not offering it is the odd choice. Anticoagulants are the interaction that is specific to goserelin rather than to the class, because of the implant needle and the documented risk of abdominal vascular injury - discuss timing of anticoagulation around insertion rather than proceeding blind. Gonadorelin is inert against a downregulated receptor. In premenopausal breast cancer, goserelin is routinely combined with tamoxifen or an aromatase inhibitor, which only works because goserelin has removed ovarian oestrogen production first.

Against leuprolide and triptorelin, goserelin achieves the same castration on the same timeline, and the choice between them is usually institutional habit, formulation interval and how the patient tolerates the administration. The implant means nothing to reconstitute and no mixing errors, at the price of a genuinely more uncomfortable insertion and a documented vascular risk. Against degarelix, goserelin is slower and flares, and the antagonist wins where a flare is dangerous. Goserelin's real distinction in this class is breadth of indication: it is the agent with randomised evidence for ovarian protection during chemotherapy, which is a use case none of the others own, and it has a longer track record in premenopausal breast cancer than the alternatives.

$200–$700/month. Zoladex has commonly been priced in the several-hundred-dollar range per 3.6 mg implant in the US, with the 10.8 mg three-monthly implant costing more per unit but similar per month. It is administered by a clinician and there is no self-supply route. Figures are indicative and were not verified in this session.

• ?The three-letter sequence is reconstructed from the D-Ser(tBu)6 and azaglycine amide substitutions described in the Core record rather than re-verified against a primary structural source in this session.
• ?The tmax figure of 336 hours is the 14-day midpoint of the label's 12 to 15 day range in men. In women the range is 8 to 22 days, so a single number is a poor summary.
• ?Terminal half-life is not stated as a discrete parameter in the label section retrieved; the 4-hour figure carried in the Core record was not confirmed here.
• ?The 27.3 percent protein binding figure comes from a single sample according to the label, which is a thin basis for a number that gets quoted as fact.
• ?POEMS participant numbers and duration were not resolved from the abstract in this session.
• ?Cost figures are indicative and were not verified in this session.

• Goserelin for ovarian protection during breast-cancer adjuvant chemotherapy Moore HCF, Unger JM, Phillips KA, Boyle F, Hitre E, Porter D, Francis PA, Goldstein LJ, Gomez HL, Vallejos CS, Partridge AH, Dakhil SR, Garcia AA, Gralow J, Lombard JM, Forbes JF, Martino S, Barlow WE, Fabian CJ, Minasian L, Meyskens FL Jr, Gelber RD, Hortobagyi GN, Albain KS, New England Journal of Medicine, 2015 · PMID 25738668

  The POEMS trial. Randomised evidence that goserelin during chemotherapy protects ovarian function and improves later pregnancy rates.

• ZOLADEX (goserelin acetate implant) - FDA prescribing information DailyMed / FDA

  Source of the 12 to 15 day tmax in men, 27.3 percent protein binding, the sex difference in clearance, and the over 90 percent urinary excretion. Also carries the inferior epigastric artery injury warning.