⚠️ Key point: Goserelin (Zoladex) causes an initial hormonal “flare” with a transient rise in testosterone or oestrogen before receptor down-regulation occurs.
This can transiently worsen symptoms (e.g. bone pain, cord compression risk in prostate cancer), so it is given with a short course of an anti-androgen such as bicalutamide initially.
- Goserelin is a synthetic analogue of luteinising hormone-releasing hormone (LHRH), also known as gonadotropin-releasing hormone (GnRH).
- It is administered as a subcutaneous depot implant given every 1 or 3 months.
- Used primarily in hormone-sensitive malignancies and certain gynaecological conditions to achieve a reversible chemical castration.
⚙️ Mechanism of Action
- Initially stimulates pituitary release of LH and FSH, causing a brief rise in sex hormones (testosterone or oestrogen).
- Continuous exposure then leads to down-regulation of GnRH receptors in the pituitary gland.
- This suppresses LH/FSH secretion, causing marked reduction in gonadal steroid synthesis — effectively producing a hypogonadal state.
🎯 Indications
- Advanced prostate cancer — suppression of testosterone production.
- Premenopausal breast cancer — suppression of oestrogen production.
- Endometriosis — to induce temporary ovarian suppression and symptom control.
- Uterine fibroids — pre-surgical reduction of fibroid size.
- Assisted conception — used for pituitary down-regulation in IVF cycles.
💊 Dose and Administration
- Subcutaneous implant:
- 3.6 mg every 28 days (monthly formulation), or
- 10.8 mg every 12 weeks (3-monthly formulation).
- Initial dose should be co-administered with an anti-androgen (e.g. bicalutamide) for 2–3 weeks to prevent symptom flare in prostate cancer.
- Administer into the anterior abdominal wall using the prefilled Zoladex implant device.
- If unfamiliar, always refer to the manufacturer’s datasheet for technique and dosing schedule.
⚠️ Contraindications
- Pregnancy and breastfeeding — teratogenic risk.
- Hypersensitivity to GnRH analogues.
💥 Side Effects
- Initial “flare” effect: transient rise in sex hormones causing increased bone pain, haematuria, or cord compression risk.
- Hot flushes, sweating, fatigue.
- Decreased libido and erectile dysfunction (men) or vaginal dryness and mood change (women).
- Gynaecomastia in men; osteoporosis with prolonged use.
- Emotional lability, headaches, weight gain.
🧠 Teaching Point
Goserelin elegantly demonstrates endocrine feedback physiology.
Continuous GnRH stimulation paradoxically suppresses gonadal hormone production by desensitising pituitary receptors.
This principle underpins “medical castration” in hormone-responsive cancers, offering the reversibility and safety of pharmacological control without surgery.
However, the initial surge phase mandates co-administration of an anti-androgen or close supervision to avoid metastatic flare.
📚 References
