Makindo Medical Notes

⚠️ 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.

📘 About: Always check the BNF link here

• 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

• BNF: Goserelin
• NICE CKS: Prostate Cancer
• Zoladex Summary of Product Characteristics (AstraZeneca)