1. Clinical Overview
Goserelin acetate is a synthetic decapeptide analogue of luteinizing hormone-releasing hormone (LHRH or GnRH). It acts as a potent GnRH agonist. Following an initial transient stimulation of the pituitary-gonadal axis (flare-up), continuous administration leads to a sustained suppression of gonadotropin secretion (LH and FSH), resulting in a profound reduction of sex steroid (testosterone and estrogen) levels to castrate or post-menopausal ranges. The 3.6mg subcutaneous implant is designed for monthly administration.
| Onset | Duration | Bioavailability |
|---|---|---|
| Initial gonadotropin surge occurs within 1-2 hours. Downregulation and significant suppression of sex steroids typically occurs within 2-4 weeks of the first dose. | The pharmacological effect on hormone suppression lasts for approximately 28 days, necessitating monthly administration. | Approximately 100% following subcutaneous implantation, as it is designed for sustained release directly into the systemic circulation. |
2. Mechanism of Action
Goserelin is a potent agonist of gonadotropin-releasing hormone (GnRH) receptors in the anterior pituitary. Continuous, non-pulsatile stimulation desensitizes these receptors, leading to downregulation. This inhibits the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In males, the reduction in LH causes a fall in testicular testosterone production. In females, the reduction in FSH and LH leads to a suppression of ovarian follicular development and estrogen production.
3. Indications & Uses
- Palliative treatment of advanced carcinoma of the prostate (Hormone-sensitive and castration-resistant stages)
- Management of advanced breast cancer in pre- and perimenopausal women suitable for hormonal manipulation
- Endometrial thinning prior to endometrial ablation for dysfunctional uterine bleeding
- Treatment of endometriosis, typically for a period of 6 months maximum
4. Dosage & Administration
Adult Dosage: 3.6 mg administered as a subcutaneous implant into the anterior abdominal wall every 28 days. For endometriosis/fibroids, treatment is usually limited to 6 months.
Administration: For subcutaneous use only. Using the pre-assembled syringe applicator, inject the implant subcutaneously into the anterior abdominal wall, alternating sites each month. Ensure aseptic technique. The implant does not need to be removed, as it is biodegradable.
5. Side Effects
Common side effects may include:
- Hot flushes (flashes) - very common in >50%
- Decreased libido and sexual dysfunction
- Sweating
- Headache
- Gynecomastia or breast tenderness/pain
- Injection site reactions (pain, erythema, bruising)
- Fatigue
- Mood swings, emotional lability, depression
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Drugs that prolong QT interval (e.g., Antiarrhythmics - amiodarone, sotalol; Antipsychotics; Fluoroquinolones) | Additive risk of QT prolongation and cardiac arrhythmias. | Major |
| Other sex hormone therapies (e.g., testosterone, estrogen supplements) | Antagonizes the therapeutic effect of Goserelin. | Major |
| Corticosteroids (long-term, systemic) | Additive risk of osteoporosis and bone loss. | Moderate |
| Drugs metabolized by CYP450 enzymes | Goserelin is not a known inducer/inhibitor, but hypoestrogenic/hypogonadal state may alter drug metabolism indirectly. Clinical significance unclear. | Minor |
7. Patient Counselling
- DO report severe or persistent injection site reactions.
- DO inform all your doctors and dentists that you are on this medication, especially before any surgery.
- DO use non-hormonal contraception (barrier methods) if you are a woman of childbearing potential.
- DONT miss your 28-day injection schedule. Mark it on a calendar.
- DONT stop the medication without consulting your specialist, even if you feel better.
8. Toxicology & Storage
Overdose: Acute overdose is unlikely due to the depot formulation. Expected symptoms would be an exacerbation of pharmacological effects: severe hot flushes, nausea, headache, and potentially severe hypoestrogenic/hypogonadal effects.
Storage: Store in a refrigerator between 2°C and 8°C. Do not freeze. Protect from light. Keep in the original package until use. The product can be kept at room temperature (not above 25°C) for a maximum of 3 months prior to use. Once removed from the refrigerator and allowed to reach room temperature, it should not be re-refrigerated. Keep out of reach and sight of children.