Class & Mechanism:
- Gonadotropin-Releasing Hormone (GnRH) agonist (also called LHRH agonist).
- Continuous administration → initial surge in LH/FSH (flare effect) → downregulation of pituitary GnRH receptors → suppressed LH/FSH release → ↓ estrogen (in females) or ↓ testosterone (in males).
- Result: medical castration — reversible suppression of sex hormone production.
Oncology Indications:
- Breast cancer:
- Premenopausal women with ER+ breast cancer — ovarian suppression in combination with tamoxifen or aromatase inhibitors.
- Risk reduction in high-risk premenopausal patients when ovarian suppression is desired.
- Prostate cancer:
- Advanced/metastatic prostate cancer — androgen deprivation therapy (ADT).
- Other uses: Endometrial cancer, gynecologic malignancies (off-label).
Formulations & Dosing:
- Depot implant (subcutaneous):
- 3.6 mg every 28 days OR
- 10.8 mg every 12 weeks
- Injected into the anterior abdominal wall.
Pharmacist Considerations:
- Tumor flare risk:
- In prostate cancer, initial testosterone surge may worsen symptoms (bone pain, urinary obstruction, spinal cord compression) — consider short course of antiandrogen before starting.
- In breast cancer, estrogen flare is less clinically problematic but may cause transient symptom worsening.
- Adverse effects:
- Common: hot flashes, mood changes, decreased libido, injection-site reactions.
- Long-term: bone mineral density loss, metabolic changes (lipids, insulin resistance), cardiovascular risk.
- Monitoring:
- Bone health (DEXA scans, calcium/vitamin D supplementation).
- Signs of osteoporosis, metabolic syndrome.
- PSA/testosterone in prostate cancer; estradiol suppression in breast cancer if indicated.
- Counseling:
- Explain flare phenomenon and possible symptom worsening initially.
- Stress adherence to injection schedule for continuous suppression.
- Importance of bone health and lifestyle modifications (weight-bearing exercise, nutrition).